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.