A lens barrel includes a first member which has a first sliding-contact surface and an opening formed in the first sliding-contact surface; a second member which has a second sliding-contact surface and moves relative to the first member, the second sliding-contact surface being placed in sliding contact with the first sliding-contact surface; a photodetector provided in the opening of the first member, facing the second sliding-contact surface, to detect relative movement between the first member and the second member; and a lubricant sump portion which, being provided in the first member, has a lubricant sump space on opposite sides of the opening interposing the opening therebetween in a direction of the relative movement.