A lens barrel 10 comprises a fourth lens group unit 20, cam pins 22a and 22b, a biasing pin 23, a cutout portion C1, a substantially cylindrical first lens group unit 13, and a plurality of rectilinear guide portions 25. The fourth lens group unit 20 has a substantially cylindrical main body portion 21 that holds a lens L4a, etc. The cam pins 22a and 22b are provided to the fourth lens group unit 20, protrude in the radial direction, and engage in the cam grooves 14b of the cam frame 14. The biasing pin 23 is provided to the fourth lens group unit 20, is supported so as to bias in the radial direction, and engages in the cam groove 14b. The cutout portion C1 is formed by cutting out the portion of the main body portion 21 of the fourth lens group unit 20 opposite the biasing pin 23 in the direction of the optical axis. The main body portion 21 of the fourth lens group unit 20 is provided continuously in the circumferential direction, from the biasing pin 23 to the cam pins 22a and 22b.