To provide an on-off valve good for uniform heat and superior in corrosion resistance.

The on-off valve comprises a valve body 12 having a first port 20 and a second port 22 into which pressure fluid is distributed, a valve disc 46 for opening/closing a communication passage between the first port 20 and the second port 22 under the displacing operation of a piston rod 32, first-to-third heaters 54b (54a, 54c) provided on the outer wall face of the valve body 12 for heating, and temperature control means 56b (56a, 56c) for controlling the heating temperatures of the first-to-third heaters 54b (54a, 54c). The valve body 12 integrally consists of an inside valve body 12a formed of a low heat conductivity material including a stainless steel and an outside valve body 12b formed of a high heat conductivity material including an aluminum alloy.