An oil tank has return oil from a hydraulic circuit diffused onto a surface of oil stored in a tank body, and thereby the return oil is prevented from going deep in the oil, so that a hydraulic pump is prevented from sucking oil containing air bubbles. The oil tank includes: an intake port provided in the vicinity of a bottom of the tank body and connected to the hydraulic pump of a hydraulic circuit; and an return oil inlet connected to a return pipe of the hydraulic circuit through which the return oil enters the tank body. In the tank body, a container adapted to hold the return oil is provided. The container is configured so that the return oil inlet opens in the vicinity of the bottom of the container.