To provide a method of fixing a piston, which can improve yield of materials.

In this piston fixing method, a piston 10, which has a recess 12 for storing a seal member 21 for partitioning a first and second hydraulic chambers R1 and R2 of a hydraulic cylinder 7 and for sealing the first and second hydraulic chambers R1 and R2, is fixed to a rack shaft 4 of a vehicle. Here, a section corresponding to the bottom of the recess 12 is caulked in a groove 4a made at an outer periphery of the rack shaft 4 by pressing the bottom of the recess 12 of the piston 10.