To provide a cut-off valve advantageous for increasing closing property for a valve element to close, airtight, a valve port by suppressing that the attitude of the valve element is radially displaced from a fixed position, and a fuel cell system.

This cut-off valve comprises an inlet port 38 and an outlet port 3, the valve element 51 capable of opening/closing the valve port 30, and an operation part 35 operating the valve element 51 in the opening or closing direction. The valve element 51 comprises a shaft part 50 inserted into the valve port 30 so as to be operated integrally with the valve element 51 and having a tip part extended in a direction back away from the operation part 35 more than the valve element 51. A guide member 80 disposed in the valve port 30 is installed so as to be back away from the operation part 25 more than the valve element 51. The guide member 80 guides the shaft part 50, and suppresses that the shaft part 50 is displaced in the radial direction of the valve port 30.