A follower mechanism for a variable gauge bogie, said mechanism comprising a follower connecting piece (1), unlocking pieces (2, 3) located on two sides of the follower connecting piece (1) and movably connected to the follower connecting piece (1), a lateral displacement identification apparatus movably connected to the unlocking pieces (2, 3), a toothed locking positioning apparatus mounted on the follower connecting piece (1), and at least two mutually parallel fixing pieces (4, 5). The follower connecting piece (1) is slidably mounted with the fixing pieces (4, 5), end portions of the unlocking pieces (2, 3) are fixedly connected to sliding pieces (201, 301), and the toothed locking positioning apparatus is respectively movably connected to the lateral displacement identification apparatus and the fixing pieces (4, 5). A brake caliper unit comprises a mounting bracket (12), the follower mechanism, and a brake execution mechanism (13) mounted on the mounting bracket (12), the follower connecting piece (1) being mounted with the brake execution mechanism (13), the fixing pieces (4, 5) being fixedly mounted on the mounting bracket (12). The brake caliper unit mechanism can automatically identify a train variable gauge, move with respect to a wheel by means of elastic force stored up by the follower mechanism and the unlocking pieces, and perform self-locking at a target gauge position, so as to implement a change in position. Also provided is the brake caliper unit for a variable gauge bogie, said unit comprising the described follower mechanism