Valve timing control apparatus for internal combustion engine

A valve timing control apparatus for an internal combustion engine, comprising:

• a cam phase actuator including a first rotor rotatable in synchronism with a crank shaft of an internal combustion engine, a second rotor fixed on a cam shaft for opening and closing an intake valve or alternatively an exhaust valve of said internal combustion engine, and a lock mechanism for locking said second rotor to said first rotor at a first relative angle in a locked state of said lock mechanism;
• an oil pump for generating a hydraulic pressure for said internal combustion engine;
• arithmetic means for arithmetically determining a current value for releasing said locked state at said first relative angle to thereby shift said first relative angle to a second relative angle;
• and
• hydraulic pressure regulating means for supplying a hydraulic pressure for regulating a cam phase of said second rotor,
• wherein said arithmetic means is so designed as to determine discriminatively said locked state and an unlocked state of said lock mechanism to thereby allow said second rotor to be released from the state locked to said first rotor when said lock mechanism is determined as being in said locked state.