To provide an earth tremor detecting power source breaker which solves a problem that an ordinary household has no countermeasure for a feared frequent earthquake and which can make a sensitivity adjustment after installation in a simple way so that the same can easily be used for every family and for all electric appliances and gas units respectively and which has a reduced cost by making simple a structure of an electric circuit.

The earth tremor detecting unit is provided with a magnet of a same polarity on a bottom side and a magnet of different polarity on an upper side in order that the magnet can be suspended in a nonmagnetic pipe by utilizing a repulsive force of the same polarity of magnets. If the detecting unit tremors, the suspended magnets move up and down and right and left and this principle is utilized. A conductive piece for establishing a circuit electrically is housed in a mini-pipe, and one electric on-off switch is provided and if a tremor occurs and it is detected, a contact circuit of the on-off switch is formed. Furthermore, a sensitivity adjustment after installation is made by a nut for a height position adjustment provided on a screwed holder of a suction magnet on the upper side.