Provided is a technique that can more reliably suppress erroneous determination of noise as an earthquake, in a seismic sensor. The seismic sensor operates in a power saving mode and a measurement mode with higher power consumption than that of the power saving mode. The seismic sensor includes: a measurement unit configured to measure acceleration; an earthquake determination unit configured to determine whether or not an earthquake has occurred based on the acceleration measured in a predetermined determination period after shifting to the measurement mode when shifting from the power saving mode to the measurement mode in a case where acceleration measured by the measurement unit exceeds a predetermined threshold; and an index calculator configured to calculate an index value indicating a scale of an earthquake in an earthquake processing period after the predetermined determination period, when the earthquake determination unit determines that an earthquake has occurred. The earthquake determination unit determines an occurrence of an earthquake based on the presence or absence of a pulse waveform in a waveform of acceleration measured in the determination period, and/or a frequency characteristic or a convergence characteristic after the pulse waveform in a waveform of the acceleration.