TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The amount of the plasticizer is 10-300 parts mass with respect to 100 parts mass hydroxyl-containing polyether which is manufactured. The plasticizer is polyoxyalkylene compound (Z') which is a polyoxyalkylene compound having the polyoxyalkylene chain derived from an alkylene oxide, and polyoxyalkylene compound which does not have a reactive group by which ring breakage addition reaction of the cyclic ether compound is carried out. The polyoxyalkylene compound is a polyoxyalkylene compound which has a deactivating group having a urethane bond, a deactivating group containing a halogen atom, and one or more terminal groups chosen from 2-8C acyloxy group and 1-8C alkoxy group at the terminal of the polyoxyalkylene chain. The polyoxyalkylene compound is a polyoxyalkylene compound of molecular weight of 100-2000 per terminal group obtained by converting the hydroxyl group of a hydroxyl-containing polyoxyalkylene compound (z1) into an alkoxy group. The hydroxyl-containing polyoxyalkylene compound (z1) has polyoxyalkylene chain derived from 2-4C alkylene oxide, and has 1-3 hydroxyl groups. All the terminal groups of polyoxyalkylene compound (Z') are methoxy groups, and alkylene oxide in the polyoxyalkylene compound (Z') is propylene oxide and/or ethylene oxide. Alternately, the polyoxyalkylene compound (Z') is a polyoxyalkylene compound of molecular weight of 100-1000 per terminal group obtained by converting the hydroxyl group of the hydroxyl-containing polyoxyalkylene compound (z1) into 1-4C alkoxy group. The amount of the polyoxyalkylene compound (Z') used is 10-80 parts mass with respect to 100 parts mass hydroxyl-containing polyether. The weight average molecular weight of the hydroxyl-containing polyether is 15000-500000. The hydrolyzable silyl group-containing compound is a compound which has an isocyanate group and hydrolyzable silyl group. Preferred Process: A compound which has active hydrogen containing group and hydrolyzable silyl group reactive with isocyanate group is reacted with the urethane prepolymer which has an isocyanate group, to obtain the hydrolyzable silyl group containing polyether.