To efficiently prevent the temperature rise of a gear and a shaft member without increasing the number of components.

This drive mechanism 10 comprises the shaft member 12, and the driven gear 11 rotatably arranged on the shaft member 12. The shaft member 12 is fixed to a face-plate member 2 in the drive mechanism 10. A flow path 12a is provided passing through the shaft member 12 along the axis of the shaft member, where gas can distribute. A space portion 14a is formed in a bearing portion 14 of the driven gear 11 in the state of being isolated from the shaft member 12.