A seismic sensor detects an earthquake with at least a predetermined magnitude and outputs a predetermined signal. The sensor includes an acceleration measurement unit that measures an acceleration applied to the seismic sensor, a velocity calculation unit that calculates a velocity response value using the acceleration measured by the acceleration measurement unit, an earthquake determination unit that determines whether the velocity response value is greater than or equal to a predetermined threshold, and an output unit that outputs the predetermined signal when the velocity response value is determined to be greater than or equal to the predetermined threshold.