An adaptor, a light source device using the adaptor, and a lighting apparatus using the adaptor are provided. The adaptor includes a main body, a protruding part, and an operating component. The main body includes: a power supply mounting part, a light source mounting part, and a conducting circuit extending from the power supply mounting part to the light source mounting part; the protruding part is operatively movable to a blocking position for blocking the power supply mounting part from being engaged with the power supply module, and a releasing position for releasing the power supply mounting part to be engaged with the power supply module. The operating component is operatively movable on the main body to an on-position and an off-position.