PURPOSE: To withstand breakdown while being compact and supply intense output signals by composing a sensor of a cantilever with piezoelectric polymer foil bonded to each surface of a conductive substrate, and oscillating the tree end of the cantilever by body acceleration received by the sensor so as to generate measurable potential on the surface of the cantilever.

CONSTITUTION: A cantilever 52 is made a conversion element of a sensor 50, and the cantilever 52 has a free end 55 and a fixed end 53 fixed by a fitting assembly 54. The free end 55 of the cantilever 52 is vertically oscillated in response to body acceleration, while the fixed end 53 is fixed into a specified position by the assembly 54. In order to generate even more intense output signals, a mass assembly 56 is provided at the free end 55 of the cantilever 52. The assembly 56 has first mass 58 on the upper side surface of the cantilever 52, second mass 60 on the lower side surface, and a mass holder 62 for fitting them. The cantilever 52 is inserted in a space made with a protrusion 66 extended from first and second supporting members 64, 68. A fitting holder 70 pressure-fixes the protrusion 66 and the member 64 to the surface of the cantilever 52. The member 68 is held between the assemblies 54, 56 and formed into such shape as to supply large output signals.