PURPOSE: To improve the frequency of using a tank and make a discharge system compact by removing a residual fluid in the tank due to the mal-function of a detection sensor.

CONSTITUTION: This detection device of fluid comprises a main block system 41 with a tube hole 42 and a screw hole 43 which is orthogonal with the tube hole 42 and tube 34 which penetrates the tube hole 42 and permits passage of a non-phototransmissive fluid. In addition, the device is equipped with an optical fiber 36 of the light emitting side which is screwed into the screw hole 43 in such a manner that the tube 34 is sandwiched between both sides of a diametral direction, an optical fiber 37 of the light receiving side, and a sensor control part which sends light into the optical fiber of the light emitting side and at the same time, detects the presence of the non-phototransmissive fluid in the tube in accordance with the level of a detected light from the optical fiber of the light-receiving side.