To provide a four-way selector valve of a tank lorry in which flow is made smooth in a gravity delivery position, flow rate becomes fast, unloading is quickened, and in addition, they are simply, easily realized.

A four-way selector valve 11 is arranged in the piping between a bottom valve and a delivery valve. By rotationally displacing and linearly moving a valve element 3 in a valve casing 2, three positions of the gravity delivery position not going through a pump, a pump delivery position going through the pump, and a pump suction position going through the pump can be switched. A side enlarging space 20 wider toward the side between a first port A and a second port B is formed in the valve casing 2, and in gravity delivery, the valve element 3 evacuates in the side enlarging space 20 by linear movement and occupies the gravity delivery position. Flow from the first port A to the second port B is linearly formed without positioning of the valve element 3 on route.