In a pressure booster having a cylinder mechanism, a floating mechanism is disposed between pistons and a piston rod, the floating mechanism being capable of absorbing offset (off centered) loads that are imposed on the pistons from the piston rod. The floating mechanism is constituted from swing bolts connected to both ends of the piston rod, support plates mounted onto end surfaces of the pistons and which swingably support the swing bolts therein, and fixing plates disposed between the ends of the piston rod and the support plates.