side thereof is disposed a speed changing mechanism for the hst the hydraulic pump thereof is positioned substantially in the lateral and longitudinal center of the housing differential gear unit 23 is disposed in an enlarged portion of the housing a brake disc 19 is fixed on the utmost end of motor shaft 4 in second chamber r 2 as shown in fig1 15 16 and 17 a brake pad 29 and a wedge shaped member 70 are interposed between the upper portion of the front surface of brake disc 19 and the inner surface of upper half housing 1 and are supported thereto movable only in the direction of the rotational axis of motor shaft 4 in a space surrounded by inner wall 8 and the surface of brake disc 19 opposite to brake pad 29 at the left side of brake disc 19 in fig1 a biasing member 72 and a brake operating shaft 14 are disposed brake operating shaft 14 is vertically disposed and is rotatably supported by upper half housing 1 and lower half housing 2 the upper end of brake operating shaft 14 projects upwardly from the housing and has a brake arm 27 fixed thereto on an outside surface of an intermediate portion of brake operating shaft 14 in the housing is formed a flat cutout 14 a which is d like shaped when viewed in cross section arch like biasing member 72 is fitted into cutout 14 a and is.