By preventing a twist of the diaphragm when assembled, various adverse effects arising from such a twist of the diaphragm are completely eliminated. Provided is a set of jigs for assembling a valve including a pair of above and below fixing jigs, a rotation-stop jig, and a fixing means: the rotation-stop jig is inserted and fixed to the above fixing jig in a non-rotational state; the fixing means fixes non-rotatably and attachably the rotation-stop jig and a bonnet of the valve to each other; a body of the valve is inserted and fixed to the below fixing jig in a non-rotational state; the bonnet and the body are fixed independently from each other in a non-rotational state, thereby preventing an outer periphery of a diaphragm from twisting in which a lower surface of an outer periphery of the bonnet and an outer seal part of the body are tightly attached to and hold the outer periphery of the diaphragm.