As for a reference valve timing varying rate A obtained by a deviation .DELTA..phi. between a target VVT phase .phi.T and an actual VVT phase .phi., when a varying rate .DELTA..theta.th of an accelerator opening degree resulting from the manipulation of the driver is relatively low, a VVT-ECU places a limit on the valve timing varying rate. When the varying rate .DELTA..theta.th of the accelerator opening degree is relatively high, it varies the valve timing with the reference valve timing varying rate A.