In an oil pan inner tank valve structure, a disc-shaped float valve is arranged below a valve port that provides fluid communication between the inside and outside of a bottom wall of an inner tank, and a lower cover is arranged below the float valve. In addition, a center recess is depressed at a lower surface center of the float valve, and a lateral movement restricting pin is upright from the lower cover and is constantly engaged with the center recess by recess/protrusion engagement. The lower cover restricts a vertically movable range of the float valve. In addition, the lateral movement restricting pin restricts lateral movement of the float valve so that a top portion of an upper surface bulged portion vertically constantly faces an area inside a valve seat.