A lens barrel including: an imaging optical system; a tube configured to contain the imaging optical system; a holder configured to hold a lens included in the imaging optical system in the tube in such a way that the lens is movable along a direction of an optical axis of the imaging optical system; a sensor unit configured to output a cyclic detection signal whose peak value changes depending on a movement amount of the holder; a memory unit configured to store a relationship between peak values of the detection signal and a position of the holder in the direction of the optical axis in advance; and an arithmetic processor configured to calculate a position of the holder in the direction of the optical axis from a peak value of a detection signal detected by the sensor unit in movement of the holder based on the relationship stored in the memory unit.