A light source-optical fiber coupler constituted by: a light source ; and a gradient index rod lens 14 for coupling diffuse luminous flux emitted from the light source to an end surface of an optical fiber. In some embodiments the medical devices can be locked in a fully deployed and locked configuration. A housing is provided, in which the gear shift gate is mounted with the selector lever pivotably in such a way that shifting between a predetermined gear of the first shift gate and a neutral position of the second shift gate is made possible.