Abstract: A transmission comprises a main shaft, a first countershaft parallel to the main shaft, a second countershaft disposed rotatably over the first countershaft, a third countershaft disposed coaxially with the first and second countershafts, first-third gear trains and a reverse gear train disposed rotationally between these parallel shafts, and a planetary gear train whose carrier is connected to the first countershaft, whose sun gear is connected to the second countershaft, and whose ring gear is connected to the third countershaft. The transmission comprises first-fourth clutches connecting or disconnecting the first-third gear trains and the reverse gear train to or from the main shaft and the first and second countershafts, a fifth clutch connecting the carrier and the sun gear or disconnecting them from each other, and a brake holding the sun gear stationary, the transmission realizing seven forward speed ranges and a reverse range.