PURPOSE: To reduce manufacturing cost of a valve by a method wherein after a valve body part and a valve cylinder part are blow-molded in a unitary body it is cut off and a valve hole is made on the valve body part.

CONSTITUTION: A molded article having an air-blowing hole 8 for blow-molding is manufactured as a unitary body in which an opening of a cylinder body 1 of a valve body part A and one end of a cylinder body 5 of a valve cylinder part B are connected. This molded article obtained by blow-molding is cut off at a cutting mark part 9, separated into a valve body part A and a valve cylinder part B and a valve hole 11 is made on the valve body 1. In the valve body part A and the valve cylinder part B which have been separated, a step part 10 and a blowing hole 8 are cut away, one end part having a closed part 4 of the valve body part A is forced to push into the opening of the valve body 5 of the valve cylinder part B and the closed part 4 is inserted into a swollen cylinder part 7.