A viewfinder 3 includes a finder optical system S2 including first and second lens groups L1, L2; a zoom frame 6 provided with first and second cam grooves 63, 64 configured to rotate about an optical axis A2 to move the first and second lens groups L1, L2 in the optical axis direction in accordance with the shapes of the first and second cam grooves 63, 64; and a diopter adjuster 9 configured to adjust the diopter of the finder optical system S2. The diopter adjuster 9 changes the position of the zoom frame 6 in the optical axis direction to adjust the diopter of the finder optical system S2, and adjusts, during rotation of the zoom frame 6, the position of the zoom frame 6 in the optical axis direction such that the diopter of the finder optical system S2 is maintained.