To prevent the occurrence of detective operation due to freezing of a solenoid valve to control a fluid pressure by a method wherein during a time in which no drive current is fed to a solenoid valve, a pulse current is fed to a drive winding in a duty ratio below the working limit of the solenoid valve.

When an atmosphere temperature is decreased to a value lower than a given value, a working switch 9 is automatically closed, a power source is fed to a source input terminal 8 from a source battery 7 and simultaneously, a display lamp 10 lights and displays that a pulse current generator 4 is in an operation state. Meanwhile, an output from a drive circuit 1 is fed to the control input terminal 5 of the pulse current generator 4 and a solenoid valve drive current is fed to the drive winding 3 of a solenoid valve 2. Further, the pulse current generator 4 feeds a pulse current in a duty ratio, being below the working limit of the solenoid valve 2, to the drive winding 3 during a time in which no drive current is fed to the drive winding 3 of the solenoid valve 2 from a drive circuit 1. This constitution performs heating by a low consumption power and prevents freezing of the solenoid valve 2 during low temperature operation.