An insertion device includes a channel defining portion extended through an inside of an insertion section up to a base portion toward a distal direction and defining a channel that is open to an outside of the insertion section in an opening of an outer peripheral portion of the base portion, and a driving unit extended through an inside of the channel with a driving axis being an axial center and being rotatable in directions around the driving axis when driven. The insertion device includes a driving force receiving portion connected to a gear portion in the opening of the channel, and a support unit supporting the driving unit so that the driving axis is parallel to the longitudinal axis in the gear portion.
