PURPOSE: To eliminate the deviation of directional sensitivity by forming detection section made up of a first conical contactor fixed on pendulum weight and a second ring-shaped contactor arranged on the circumferential surface thereof facing it.

CONSTITUTION: A detector 15 is provided on the top surface of a pendulum weight 3 so fixed at the tip of a bar-shaped spring 4 as to oscillate horizontally with an earth quake by way of a rod member 6. A truncated-cone shaped contactor 15A is mounted to a rod member 6 while a ring-shaped contactor 15B is fixed on a case 2B through a support device 17 surrounding thereof. The separating space between the contactors 15A and 15B can be adjusted by vertically moving the case 2B with a screw. The circumferential endless arrangement of both the contactors 15A and 15B can be eliminate deviation of the directional sensitivity. The fine adjustment of the space between the contactors also can simplify the setting of the value.