A back-plate composition of the present invention is a composition for forming a back plate of a brake pad, the brake pad having a friction material and the back plate bonded to the friction material. The back-plate composition includes a resin, a plurality of first fibers and a plurality of second fibers having an average length shorter than an average length of the first fibers. In the case where the average length of the first fibers is “L1” [μm] and the average length of the second fibers is “L2” [μm], “L2”/“L1” is in the range of 0.001 to 0.5. This makes it possible to provide a back-plate composition having excellent moldability, as well as a back plate formed of the back-plate composition, a brake pad including the back-plate and a caliper device provided with the brake pad.