A hydromechanical continuously variable speed transmission according to the present invention includes: the HST 10 in which the planetary gear mechanism 11 is housed in the planetary gear support case 71 mounted on a face of the center section 35 to form the HMT unit 100, the face being on the side opposite to the side on which the HST case 23 is mounted, and the HMT unit 100 is further provided with the housing mounting face 35d for fixing the HMT unit 100 to the housing 91 of the traveling power transmission mechanism 89, the housing mounting face 35d being provided on the center section 35 so as to surround the outer circumference of the mounting face 71a on which the planetary gear support case 71 is mounted.