PURPOSE: To insert a valve member into a valve inner cylinder and carry out centering by inserting a stopper body into the intermediate opened port part of a spool hole, tentatively inserting a spring, carrying out centering, inserting a spool, pulling out a stopper plate, and dropping a valve member.

CONSTITUTION: Positioning is performed by the fitting of the positioning projection 2A of a stipper 2 into the positioning groove 1C of a valve body 1, and at the same time, a stopper plate 3 is inserted into the intermediate opened port part 1B of a spool hole. Then, a spool 30 which is formed integrally with a spring 20 is inserted into a valve inner cylinder. At this time, the lower edge part of the coil spring 20 is centering-performed by the centering guides 3A and 3B of a stopper plate 3. Then, an outwardly spreading holder 10 rises to the degree clearing the step difference of the projection 3A or recessed part 3B, and the stopper 2 retreats rightward, and the stopper plate 3 is pulled out from the opened port part 1B. Then, the outward spreading holder 10 releases the upper edge holding of the spool 30, and the coil spring 20 and the spool 30 are formed integrally, and dropped vertically, and the insertion work is completed.