Described herein is a brake support mechanism particularly suitable for use in a 4-wheel drive auxiliary transmission to reduce the axial dimensions and to facilitate assembling of the transmission, the brake support mechanism essentially comprising: a transmission case; a cylindrical rotary member mounted in the transmission case; a multiple disk brake constituted by a combination of brake plates splined on the inner periphery of the transmission case and brake disks splined on the outer periphery of the rotary member; a center support fitted in the transmission case in a position adjacent the multiple disk brake; and a hydraulic actuator including an annular cylinder formed in the center support on the side of the multiple disk brake, a piston slidably fitted in the cylinder, an operating fluid supply passage formed in the center support, a return spring located on the outer periphery of the multiple disk brake and having one end thereof abutted against the transmission case, and a return spring mounting member connecting the other end of the return spring to the piston.