To set the hold current that maintains the full closing or opening condition of a valve to an optimum value despite receiving inference of its production dispersion, aging degradation and the like.

With an ignition switch on, either solenoid 5 or 6 is energized to fully close or open a valve 4 first accordingly, after which the hold current that maintains the full closing or opening condition of the valve 4 is gradually reduced and the output value of a valve lift sensor 10 is read in at the same time. The hold current when the output value of the valve lift sensor 10 suddenly changes is learned as the threshold value that holds the valve 4 fully closed or opened. Unless the ignition switch is turned off, the hold current supplied is set to 110% of the threshold value.