The invention aims to provide a coaxial reverse rotating speed and direction changing machine with compact structure, small size and light weight. An input shaft (29) is connected with a bevel gear (27); the bevel gear (27) is embedded with a bevel gear (7); the bevel gear (7) is connected with an output shaft (5); the bevel gear (7) and a gear (8) are connected gears; the gear (8) is embedded with a gear (11); a gear (12) is embedded with a gear (18); the gear (18) is embedded with a gear (22); and one part, projected out of a shell, of the gear (22) is a reverse output end. The machine is compact in structure, light in weight, low in cost and convenient for installation and maintenance, finishes speed change, transmission and reversing in a box body, and effectively prevents the defect of high fault rate due to exposure outside of such transmission and reversing devices as triangular belts and chains.