A protective device for an injection unit of an injection molding machine includes a protective plate which is disposed at an outlet port of a channel of an injection nozzle. The protective plate is moveable between a shielding position, in which the outlet port is covered, and an opening position, in which the outlet port is cleared. Moving the protective plate between the shielding and opening positions is a mechanical switching mechanism which is disposed outside the channel and applies an adjusting force which acts between the protective plate and a molding tool, when the injection unit docks on the molding tool.