A twin clutch type transmission that permits a quick shifting of a mechanical clutch without shock. Numbers of gear teeth of speed-change gears of odd and even-numbered gear ranges, which mesh with the same output gear, are made to be identical each other; gear ratios of input gear trains of even and odd-numbered gear ranges are configured so that the speed-change ratios between adjoining gear ranges will form a geometric progression; and gear ratios between speed-change gears of odd and even-numbered gear ranges are configured to be proportional to square of the common ratio. In speed-changing intermediate shaft on which the speed-change gear is installed is coupled with input shaft through friction clutch, and speeds of revolutions of the speed-change gear and the intermediate shaft on which such speed-change gear is installed are brought into synchronized state.