To enable stable detection of the magnitude of an earthquake for a long time.

This seismoscope is provided with a seismic sensing section 10 which senses vibration as caused by an earthquake to convert the vibration to changes in the pressure of a gas, a pressure change sensor section 30 to convert the pressure change into an electrical signal and a signal processing section 40 which processes a signal outputted from the pressure change sensor section 30 to judge the presence and the magnitude of the earthquake. With the rotation of a ball body 15 caused by the vibration, an oscillation body 17 moves vertically so that the pressure varies within a gas chamber 32 of the pressure change sensor section 30. An piezo-electric thin film 34 vibrates according to the changes in the pressure to induce a fine voltage. The fine voltage is amplified by an amplifier 41 of the signal processing section 40 and converted into digital from analog by an input-output port 42 to be inputted into a microprocessor 43. The microprocessor 43 compares a pattern of a signal obtained with a specified signal pattern to judge whether the change in the pressure is attributed to the vibration of the earthquake or not and also the magnitude of quake of an earthquake.