To obtain a detecting device which can reduce the scrape of an edge in a detection output corresponding to the unevenness of a magnetic rotating body due to the accuracy of the arrangement position of a magnet and that of a magnetism detecting element.

A detecting device is provided with a magnet 20 which generates a magnetic field, with a magnetic rotating body 2 which is arranged by keeping a prescribed gap from the magnet 20 and which changes the magnetic field generated by the magnet 20 and with a magnetism detecting element 3 whose resistance value is changed according to the magnetic field changing by the magnetic rotating body 2. It is constituted in such a way that an inclination is formed on the face, of the magnet 20, faces with the magnetism detecting element 3.