PURPOSE: To obtain a contact detector which is free from malfunctions and is suited for use with a toner, etc. by mounting an electro-mechanical transducer to an oscillator the surface of which is coated with a resin layer, and providing an oscillation circuit which excites the oscillator.

CONSTITUTION: When a power source is supplied to an oscillation circuit, a signal is applied to a piezoelectric element 2, and an oscillator 1 oscillates. The oscillation is detected with a piezoelectric element 3, and is positive-fed back to the circuit 4. As a result, the oscillation is continued. When the oscillator 1 is restrained of the oscillation, the positive feedback loop is interrupted and the oscillation ceases. The restraining of the oscillation is checked by the contact with an object. The surface including the elements 2, 3 of the oscillator 1 is coated with an insulation resin layer 4 at about the thickness at which the oscillation of the oscillator 1 is not suppressed.