To provide a power transmission mechanism capable of suppressing thermal expansion of members such as a gear, and of easily reducing a manufacturing cost and a space.

This power transmission mechanism comprises a connection mechanism composed by connecting a drive unit bracket 10 to a gear 3 by interlaying an arm 7 between them. The linear coefficient of expansion of the drive unit bracket 10 and that of the arm 7 are different from each other; and displacement by thermal expansion of the arm 7 in which the linear coefficient of expansion and the member length of the arm 7 is different from those of the drive unit bracket 10 is corrected by displacement in response to the temperature variation and the component length of the drive unit bracket 10 and the arm 7.