PURPOSE: To be capable of detecting oil leakage of any oils with a simple means, by providing an oil immersible light scattering material to an oil sending pipe line between a luminous part and photodetecting part.

CONSTITUTION: An oil leakage detecting element is constituted by providing a luminous part 1 and a photodetecting part 2 face to face and an oil immersible light scattering material 3 consisting of a mat or fine pulverulent body of transparent synthetic fiber or inorganic glass fiber, pulverulent body etc. Scattering of the light is extremely decreased in case of invading the oil in this light scattering material because a refractive index of the oil is about 1.40W1.50 and transmitting quantity of the light is increased. Accordingly, the light from the part 1 is detected by the part 2 and an oil leakage signal is given.