CONSTRUCTION MACHINE

A rear half part of a surface of a main body of a working oil tank installed in line with a control valve opposing to the valve is dented in an inclining surface shape in the direction moving away from the valve so that between both the tank and the valve, is formed a working space for attaching and detaching a pressure compensating spool, while return tubes are separately connected to the upper and the lower side of a filter case side wall within the body. Within the body, is provided a cylindrical filter case having a bottom in which a return filter for return oil is housed, and the return tubes are connected to the case side wall in a state of communicating with the inside of the filter case. In this configuration, a filter receiving plate is provided in a lower part within the filter case with leaving a gap between the plate and the filter case bottom wall in a state that the plate is supported by a return pipe, the return filter is disposed on the plate, and the return tubes are connected to the filter case side wall on the lower side than the plate.