With the relative positional change between a first substrate and a second substrate due to an external vibration, the positional relationship between an electret group and an electrode group changes, as a result of which a vibration sensor outputs the detection signal of the external vibration. The electrode group is divided into two or more predetermined number of phases, and small electrode groups are formed that can generate electric signals in response to the external vibration on a per-phase basis. In the electrode group, a phase difference generation gap that generates predetermined phase differences between the respective electrical signals generated in the small electrode groups is provided between adjacent electrodes included in the electrode group, according to the predetermined number of phases. The vibration sensor outputs, as the detection signal of the external vibration, a signal formed by superimposing the electric signals generated in the small electrode groups as a result of the relative positional change between the first substrate and the second substrate due to the external vibration. This provides a highly simple and convenient vibration sensor for detecting an external vibration by use of electrets.