In an electronic unit loading mechanism, an electronic unit is attachable to or detachable from an electronic unit loading base which is retractable to a housing. The electronic unit loading mechanism comprises a main part fixed to the loading base and a holding part holding the electronic unit. The holding part is vertically movable to the main part between a taken-out position and a loaded position, wherein the holding part at the taken-out position is taken out from the main part so that the electronic unit is attached to or detached from the loading base, and the holding part at the loaded position is contained in the main part so that the electronic unit is loaded to the loading base.