PURPOSE: To make it possible to use a piezoelectric device which is capable of widely handling by using an ignition agent obtained by low density processing of a specific mixture.

CONSTITUTION: When a presser pin 45 is drawn out, a metal ball 44 moves outward and a compression rod 42 strikes against a piezoelectric device 41 by the elasticity of a spring 43 to generate high voltage in the piezoelectric device 41. Discharge sparks are generated between a pair of ignition terminals 5 and an ignition agent 7 is ignited. Since the ignition agent 7 prepared by low density processing of a mixture of zirconium powder having a mean particle size of 3μm or less, fine barium chromate powder, and inorganic fibers, it is surely ignited even by very small spark energy and a thermal battery is reliably activated. The use of a detonator whose handling is limited only a qualified person is eliminated, and the thermal battery equipped with the piezoelectric device capable of widely handling can be realized.