PURPOSE: To secure the extent of synchronization for normally stabilized separate flow in a simple structure using no valve gear by reciprocating a piston by means of rotation of a cylinder barrel via a swash plate mechanism, while connecting plural supply and exhaust ports and a connecting passage respectively in a specified state.

CONSTITUTION: When an on-off valve 102 is seelcted and pressure oil out of a supply source 101 is fed to a first external connecting port 160 in a hydraulic flow synchronizer 100, this pressure oil opens a check valve 183 and flows down to respective supply and exhaust ports 143, 142 of a cover 112 from a first connecting passage 170. In addition, this pressure oil rotates a cylinder barrel 116 according to a tilt angle of a swash plate 117, and it functions as the same capacity double motor consisting of a cylinder hole 121 and a piston 131 in a first group and a cylinder hole and a piston in a second group. In consequence, since the pressure oil flows down simultaneously at the same quantity to respective actuators 103a, 103b, these identical rated ones 103a, 103b are elongated at the same speed.