NOVELTY - The reactor (1 alpha ) has a magnetic core (3 alpha ) that forms a closed magnetic circuit. The core is provided with the inner and outer core units (31,32) that are covered with and exposed without covering the coil elements (2A,2B) respectively. A supporting leg portion (320) of outer core unit is provided to support an assembly (10 alpha ) on an attachment surface by contacting attachment surface in which outer core unit protrudes in a parallel direction of coil element, and mounts assembly. An overhang portion of outer core unit is projected over a width direction of assembly.    USE - Reactor of converter used in power converter device (all claimed) such as bidirectional direct current (DC)-DC converter mounted in vehicles such as hybrid vehicle, electric vehicle, and fuel cell electric vehicle such as car.    ADVANTAGE - The width of the upward space of attachment surface is made narrow when attaching the assembly of the reactor to the narrow path-shaped attachment surface when the width of the occupancy space of reactor is made small by pulling out the edge portion of coil in the end surface direction of coil element so as to easily attach the assembly of reactor to attachment surface so that the edge portion of coil can is pulled out on the outer side of the installation space of narrow path-shaped reactor. Thus, the electric equipment is easily connected to the edge portion of coil. Hence, the reactor is effectively installed in narrow path-shaped location. The change of the shape of supporting leg portion is bent when the curved attachment surface forms convex form swollen to paper surface upper direction so that the axial direction intermediate portion of coil form convex to upward. Thus, the lower end surface of coil is prevented from interfering in the curved attachment surface.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of the reactor.    Reactor (1alpha)    Coil elements (2A,2B)    Magnetic core (3alpha)    Assembly (10alpha)    Inner and outer core units of magnetic core (31,32)    Supporting leg portion of outer core unit (320)