To obtain a process controller maintainability of which can be enhanced by prolonging the life of cooling fans uniformly thereby extending the regular replacement cycle.

The process controller comprises: a cabinet having cooling fans for constant use which cool the housed electrical components; and standby cooling fans. The process controller further comprises a cooling fan operation/stop controller which operates all cooling fans, i.e. the cooling fans for constant use and the standby cooling fans, while switching sequentially every predetermined time so that the remaining life time of all cooling fans becomes approximately equal, and then sequentially halts the all cooling fans corresponding, in number, to the standby cooling fans.