To provide a hydraulic device capable of more surely preventing any leakage of working fluid communicating between a side plate end face and a gear end face, preventing abnormal wear in the side plate from occurring, and thereby ensuring high output efficiency and silence.

A hydraulic device 1 includes: a housing 2 having a hydraulic chamber 4 formed therein; a pair of gears 20, 23 inserted in the hydraulic chamber 4 with gear teeth being engaged with each other; a pair of bushes 40, 44 for supporting rotary shafts 21, 24 of the gears 20, 23; and a pair of side plates 30, 32 to be interposed respectively between the gears 20, 23 and the bushes 40, 44. At least one island-shaped projection parts 42, 46 are formed on one mutually-opposing face out of the side plates 30, 32 and the bushes 40, 44, and the projection parts 42, 46 are made opposite to the other mutually-opposing face with a spacing. The side plates 30, 32 are swingably configured respectively with the projection parts 42, 46 as supporting points.