A hydraulic cylinder includes a rod insertion hole formed in a piston member, an auxiliary rod provided to a head side end wall member and capable of being inserted into the rod insertion hole, a rod fitting hole formed to pass through the head side end wall member and the auxiliary rod, a movable rod installed in the rod fitting hole and whose end portion toward a head side end wall projects to the exterior, a movement restriction mechanism that prohibits shifting of the movable rod in an unclamping state and permits shifting of the movable rod in a clamping state.