To provide a hydraulic/mechanical continuously variable transmission device in which the transmission case is compactified, its strength is heightened, and the HST (hydrostatic continuously variable transmission device) operating system can be compactified.

A hydraulic/mechanical continuously variable transmission device is structured so that an HST 4 and a planetary gearing mechanism are combined to perform shifting of the output rotation, wherein a casing Ca of the HST 4 arranged in front of the planetary gear mechanism is formed from an inner casing part at the forefront end of the transmission case 1 of double cylindrical structure, while a motor cylinder 18 for shifting operation of the HST 4 is installed integrally with the inner casing 16, and a pump cylinder 19 and solenoid control valves 29--are arranged in a dry chamber Sk part between the inner casing part 16 and an outer casing part 1A.