TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The resin composition further contains at least a thermosetting resin and a curing agent for the thermosetting resin, where the thermosetting resin is an epoxy resin. Preferred Components: The resin composition has a stress relaxation rate (R1) of 20-95%, and the residual strain rate ( alpha ) of 0-3%, as measured in a tensile-compression test, where: tensile-compression test is performed by using an extension-restoration test, in which a piece of resin composition (having a thickness of 50 mu m, and sample shape of number 6 type dumbbell (having a width (of measured portion) of 4 mm and a length of linear portion of 25 mm)) is subjected to an extension process and a restoration process using a tensile-compression tester in accordance with ISO 3384; the extension process is performed under conditions including deflection correction carried out at a force of less than or equal to 0.05 N (to eliminate deflection generated when the test piece is attached to a clamp), speed of testing at 25 mm/minute (0-25% extension), a temperature at 23 degrees C, and extension/holding conditions including holding for 5 minutes at 25% extension; the restoration process is performed under conditions including speed of testing at 0.1 mm/minutes (until the tensile force reaches 0 plus minus 0.05 N), and a temperature at 23 degrees C; the stress relaxation rate (R1) is calculated by a method, in which the tensile force is measured at a point when the extension process is complete (an initial tensile force (F1)), then the amount of strain is maintained for 5 minutes under the extension/holding conditions, after which the tensile force is measured (F2(t5)), hence the stress relaxation rate (R1) is equal to a value of ((F1-F2(t5))/(F1)x 100); and the residual strain rate ( alpha ) is calculated by a method, in which an amount of strain being measured at a point where the tensile force in the restoration process reaches 0 plus minus 0.05 N. In the composition, when the degree of extension is 15-20% in the extension-restoration test, the slope of the change in tensile force relative to the amount of strain during restoration and extension (slope during restoration/slope during extension) is less than or equal to 0.95. A stress value measured at a point of maximum extension (25% extension) is a maximum stress value in the extension-restoration test, and in cases where measurements are started at the point where the extension process is complete in the stress relaxation properties test, a ratio of the tensile force (F3) immediately after completion of the extension process and the tensile force (F4(t30)) 30 minutes after completion of the extension process (F4(t30)/F3) is 0.1-0.7. The stress relaxation properties test is performed by a method, in which a piece of resin composition (having a thickness of 50 mu m and a sample shape of number 6 type dumbbell (width of measured portion of 4 mm and a length of linear portion of 25 mm)) is subjected to an extension process under the conditions using a tensile-compression tester in accordance with ISO 3384, and at the point where the extension is complete, the tensile force being measured as the initial tensile force (F1), and tensile force after 30 minutes being measured as (F4(30)), where the extension process is performed under conditions including deflection correction carried out at a force of less than or equal to 0.05 N (to eliminate deflection generated when the test piece is attached to a clamp), speed of testing at 25 mm/minute (up to 50% extension), temperature at 23 degrees C, and extension/holding conditions including holding for 30 minutes at 50% extension. EXAMPLE - Typical resin composition comprised of: 100 parts by mass of A1000 (RTM: Polyrotaxane); 75 parts by mass of JER1003 (RTM: Epoxy resin); 1.1 parts by mass of 2-ethyl-4-methylimidazole; and 45 parts by mass of DN950 (RTM: Isocyanate).