To improve operation amenity and defect preventability in a lubricant dosing device for feeding an adequate dose of lubricant to a compressed air flow.

The lubricant dosing device is provided with a lubricant tank, a pneumatic lubricant pump, and an injection passage connected to the lubricant pump, and the injection passage is sealed to an outlet of the lubricant pump by a valve element of a check valve. The valve element of the check valve 7 is connected with an electronic sensor 19 so that the electronic sensor 19 generates an electric signal when the valve element (a valve plunger) of the check valve moves by a predetermined stroke, and the outlet is opened momentarily by a pressure of the lubricant generated during an injection process so that the lubricant reaches the injection passage.