A lens position calculator is provided that determines a phase of a driving signal as a reference position of an imaging lens when an output value of a position detection sensor reaches a threshold value. The lens position calculator determines a position obtained by performing addition or subtraction on the reference position read out from a reference position storage as a judgment position, detects an output value of the position detection sensor at a timing in synchronization with the driving signal that drives a driver and at the judgment position, and judges whether the output value of the position detection sensor at the judgment position reaches the threshold value or not, so as to determine the reference position again.