PURPOSE: To improve the transient response of a movable valve and the follow-up characteristics thereof toward a target value by controlling the drive means of the movable valve in such a way as to meet a specific condition depending upon a difference between the target opening of the valve optimum for an engine speed and the present opening thereof speed.

CONSTITUTION: A movable valve (g) provided in the air flow passage of an engine is driven with a means (f) depending upon the predetermined input signal. In this case, there are provided a means (a) for detecting an engine speed, and another means (b) for setting the target opening of the valve (g) depending upon the engine speed. Also, there are provided a means (c) for detecting a present valve opening and another means (d) for detecting a difference between the present opening and the target opening. And a means (e) is provided for controlling a means (f) depending upon the difference. In other words, when the difference is equal to or above the first reference value, a drive signal is continuously outputted, and the drive signal is gradually increased when the difference is between the first reference value and the second reference value less than the first reference value. And the drive signal is terminated when the difference is equal to or below the second reference value.