To provide a transmission device including an input shaft of high rigidity.

The input shaft 51 including a pinion shaft 53 includes a plurality of eccentric sections 51b which have opening sections 51e in which inner gears of an eccentric disk 52 and pinion gears 53a of the pinion shaft 53 can be engaged with each other, shift the phases of the opening sections 51e and are arranged along in a shaft direction; and extensions 51c, 51d formed on both sides of the shaft directions of the eccentric sections 51b. Moreover, the eccentric disk 52 is supported by the extensions 51c, 51d via a bearing 57 and the input shaft 51 is supported by the pinion shaft 53 via a bearing 56.