A lock determination device for variable valve timing mechanism includes means for detecting an operating position of a variable valve timing mechanism having a function of locking a valve timing of an internal combustion engine in an intermediate position between a most retarded position where the valve timing is most retarded and a most advanced position where the valve timing is most advanced in stopping operation of the internal combustion engine, means for starting a timer when the operating position of the variable valve timing mechanism enters an intermediate region, the intermediate region being a predetermined region including the intermediate position, means for determining whether or not the operating position of the variable valve timing mechanism is in a determination holding region wider on a retardation side than the intermediate region after the timer is started, means for incrementing a value of the timer if the operating position of the variable valve timing mechanism is in the determination holding region, and means for determining that the operating position of the variable valve timing mechanism has been locked in the intermediate position when the value of the timer reaches a predetermined value.