A valve device configured to control supply of hydrogen gas from a gas tank to a fuel cell mounted in a vehicle and comprising: a body having a gas passage and an accommodation hole communicated with the gas passage; and a solenoid valve accommodated in the accommodation hole;wherein the solenoid valve includes: a sleeve having a tubular shape and fitted in the accommodation hole, the sleeve including a passage (66, 68) communicated with the gas passage, an opening-closing portion configured to open and close the passage (66, 68); and a driving portion configured to drive the opening-closing portion to open and close the passage (66, 68), a seal member is disposed between an outer wall surface of the sleeve and an inner wall surface of the accommodation hole, and the body has a joint connection opening that is located downstream of the passage of the sleeve, the joint connection opening being opened on an outer surface of the body, characterized in that the valve device further comprises a joint member fixed to the body, the joint member is fixedly attached to the joint connection opening, the joint member has a communication passage connected to the passage of the sleeve, the joint member includes a backflow reduction valve configured to hinder movement of gas in the communication passage toward the sleeve, and a valve seat of the joint member is held between the body and the joint member, the outer surface of the body and the valve seat being brought into close contact with each other, and the valve seat and the joint member being brought into close contact with each other, such that a space between the body and the joint member is air-tightly sealed by the valve seat. a body having a gas passage and an accommodation hole communicated with the gas passage; and a solenoid valve accommodated in the accommodation hole;wherein the solenoid valve includes: a sleeve having a tubular shape and fitted in the accommodation hole, the sleeve including a passage (66, 68) communicated with the gas passage, an opening-closing portion configured to open and close the passage (66, 68); and a driving portion configured to drive the opening-closing portion to open and close the passage (66, 68), a sleeve having a tubular shape and fitted in the accommodation hole, the sleeve including a passage (66, 68) communicated with the gas passage, an opening-closing portion configured to open and close the passage (66, 68); and a driving portion configured to drive the opening-closing portion to open and close the passage (66, 68), a seal member is disposed between an outer wall surface of the sleeve and an inner wall surface of the accommodation hole, and the body has a joint connection opening that is located downstream of the passage of the sleeve, the joint connection opening being opened on an outer surface of the body, characterized in that the valve device further comprises a joint member fixed to the body, the joint member is fixedly attached to the joint connection opening, the joint member has a communication passage connected to the passage of the sleeve, the joint member includes a backflow reduction valve configured to hinder movement of gas in the communication passage toward the sleeve, and a valve seat of the joint member is held between the body and the joint member, the outer surface of the body and the valve seat being brought into close contact with each other, and the valve seat and the joint member being brought into close contact with each other, such that a space between the body and the joint member is air-tightly sealed by the valve seat.