A connection mechanism is provided with a shaft member formed with an outer-screw portion which is formed with an outer screw, a plate member formed with a connection hole in which the shaft member is fitted, a nut member formed with an inner-screw to engage with the outer-screw of the shaft member, the nut member engaged with the shaft member being urged toward the plate member fitted on the shaft member to fixedly secure the plate member onto the shaft member, and a fixing mechanism that fixes the plate member and the nut member with each other to retain a status where the plate member and the nut member are urged oppositely in a rotational direction about a central axis of the shaft member.
