A strainer device includes a strainer element; a first lid member that covers an upper opening of the strainer element; a second lid member that covers a lower opening of the strainer element and has a fitting hole in a portion surrounded by the strainer element; a delivery pipe protruding upward inside a hydraulic oil tank in a state in which the delivery pipe is fitted into the fitting hole of the second lid member; and a check valve arranged at the first lid member. The check valve includes a valve main body having a valve passage whose one end opens to the internal space of the strainer element and whose other end opens to inside of the hydraulic oil tank; and a valve body which is arranged to be able to move in a vertical direction with respect to a valve seat provided in the valve passage.