To solve the problem with a steering device wherein the ratio of transmission from a steering member to steered wheels does not match the taste of users since the ratio is specific to a vehicle.

A removable transmission unit 3 is installed in a steering mechanism 4. The transmission unit 3 comprises a transmission mechanism 25 having an input shaft 18 and an output shaft 19 and a housing 24 holding the transmission mechanism 25 and attachable to and detachable from a steering column 13 as the fixed part of the steering mechanism 4. The input shaft 18 may have or not have the steering member 2 beforehand. The output shaft 19 is attachable to and detachable from the input shaft 5 of the steering mechanism 4. The transmission units 3 of a plurality of specifications having different ratio of transmission from the input shaft 18 to the output shaft 19 is prepared beforehand, and the transmission unit selected from these transmission units is used for the steering device 1.