A fuel cell system including a fuel cell body; a first portion continuously supplied with heat following start up of the fuel cell body; a second portion continuously supplied with heat following start up of the fuel cell body; and a hydrogen exhaust valve. The first portion and the second portion are directly fixed to each other with the hydrogen exhaust valve disposed therebetween. The first portion is, for example, a gas-liquid separation unit supplied with heat from exhaust gas from the fuel cell body, and the second portion is, for example, a hydrogen processing unit supplied with heat from exhaust gas from the fuel cell body.