The object of the present invention is to modify the shock originated from engaging and disengaging of a clutch during acceleration, when using a mesh type transmission provided with a clutch for engaging and disengaging the shift gear and the output shaft. A mesh type automatic transmission equipped with an input shaft 300 for introducing power of an engine, a plurality of shift gears 301, 303, 304, 306, 310, a plurality of cogged clutches 302, 305, 308, an output shaft 323 for outputting driving force, a counter shaft 315, and a plurality of counter gears 314, 316, 317, 318, 322, for transmitting power of the engine to the output shaft 323 by rotating the input shaft 300 with the power of the engine, rotating the counter shaft 315 by rotation of the input shaft 300, and transmitting rotation of the counter shaft 315 to the output shaft 323 via the counter gears 314, 316, 317, 318, 322 with the automatic shifting by engaging and disengaging the cogged clutches 302, 305, 308 to one of the shift gears 301, 303, 304, 306, 310 corresponding to the speed, wherein an assist mechanism 6 for transmitting rotational force of the input shaft 300 to the output shaft 323 by transmitting rotation of the counter shaft 315 via the assist gear 325, during the period of disengagement of a gear 301, 303, 304, 306, 310 to engagement of a new gear 301, 303, 304, 306, 310 at shifting, is provided to the output shaft 323.