A dual clutch transmission comprising: a first clutch; a second clutch that is disposed concentrically with the first clutch; a first input shaft that is connected to a power source via the first clutch; a second input shaft that is a hollow shaft through which the first input shaft is inserted rotatably, the second input shaft being connected to the power source via the second clutch; a counter shaft that is disposed parallel to the first input shaft and the second input shaft; an output shaft that is disposed parallel to the counter shaft and coaxial with the first input shaft and the second input shaft; a first splitter gear changing portion comprising: a first input gear through which the second input shaft is inserted rotatably; a first counter gear that is fixed to the counter shaft and meshes with the first input gear; a second input gear through which the first input shaft is inserted rotatably; a second counter gear that is fixed to the counter shaft and meshes with the second input gear; and a first coupling mechanism configured to couple the first input gear and the second input gear selectively to the second input shaft; a second splitter gear changing portion comprising: an input/output gear; a third counter gear, the third counter gear meshing with the input/output gear; a second coupling mechanism configured to couple the output shaft to the first input shaft; and a third coupling mechanism; and an output portion comprising: a fourth counter gear that is fixed to the counter shaft; an output gear through which the output shaft is inserted rotatably, the output gear meshing with the fourth counter gear; and a fourth coupling mechanism configured to couple the output gear to the output shaft, characterized in that: the input/output gear is fixed to the first input shaft; the counter shaft is inserted rotatably through the third counter gear; and the third coupling mechanism is configured to couple the third counter gear to the counter shaft. a first clutch; a second clutch that is disposed concentrically with the first clutch; a first input shaft that is connected to a power source via the first clutch; a second input shaft that is a hollow shaft through which the first input shaft is inserted rotatably, the second input shaft being connected to the power source via the second clutch; a counter shaft that is disposed parallel to the first input shaft and the second input shaft; an output shaft that is disposed parallel to the counter shaft and coaxial with the first input shaft and the second input shaft; a first splitter gear changing portion comprising: a first input gear through which the second input shaft is inserted rotatably; a first counter gear that is fixed to the counter shaft and meshes with the first input gear; a second input gear through which the first input shaft is inserted rotatably; a second counter gear that is fixed to the counter shaft and meshes with the second input gear; and a first coupling mechanism configured to couple the first input gear and the second input gear selectively to the second input shaft; a first input gear through which the second input shaft is inserted rotatably; a first counter gear that is fixed to the counter shaft and meshes with the first input gear; a second input gear through which the first input shaft is inserted rotatably; a second counter gear that is fixed to the counter shaft and meshes with the second input gear; and a first coupling mechanism configured to couple the first input gear and the second input gear selectively to the second input shaft; a second splitter gear changing portion comprising: an input/output gear; a third counter gear, the third counter gear meshing with the input/output gear; a second coupling mechanism configured to couple the output shaft to the first input shaft; and a third coupling mechanism; and an input/output gear; a third counter gear, the third counter gear meshing with the input/output gear; a second coupling mechanism configured to couple the output shaft to the first input shaft; and a third coupling mechanism; and an output portion comprising: a fourth counter gear that is fixed to the counter shaft; an output gear through which the output shaft is inserted rotatably, the output gear meshing with the fourth counter gear; and a fourth coupling mechanism configured to couple the output gear to the output shaft, characterized in that: the input/output gear is fixed to the first input shaft; the counter shaft is inserted rotatably through the third counter gear; and the third coupling mechanism is configured to couple the third counter gear to the counter shaft. a fourth counter gear that is fixed to the counter shaft; an output gear through which the output shaft is inserted rotatably, the output gear meshing with the fourth counter gear; and a fourth coupling mechanism configured to couple the output gear to the output shaft, characterized in that: the input/output gear is fixed to the first input shaft; the counter shaft is inserted rotatably through the third counter gear; and the third coupling mechanism is configured to couple the third counter gear to the counter shaft. the input/output gear is fixed to the first input shaft; the counter shaft is inserted rotatably through the third counter gear; and the third coupling mechanism is configured to couple the third counter gear to the counter shaft.