An internal combustion engine is provided with a plurality of valves, including a main driving valve and a driven valve, each of which can be lifted in response to an instruction from a control apparatus, and a lift sensor which detects a lift amount of the main driving valve. The control apparatus controls the lift of the driven and main driving valves based on an output of the lift sensor. The engine may also include a proximity sensor which detects whether the position of the driven valve is within a predetermined range, and a crank angle sensor. The control apparatus monitors the output of the proximity sensor to determine whether the driven valve is out of synchronization with respect to the crank angle, and performs an initial driving control that initializes the positions of the driven and main driving valves corresponding to the driven valve when loss of synchronization is detected.