A rotational-rate sensor is provided which includes a detecting element, a circuit
portion, an airtight container and an elastic body, in which: the synthetic resonance-frequency
of a machine system of the rotational-rate sensor and the frequency of an applied
rotational rate which corresponds to the difference between the resonance frequency
in the direction where the detecting element is driven and the resonance frequency
of the detecting element in the direction where the detecting element detects a
rotational rate, are each lower than each of the resonance frequency in the direction
where the detecting element is driven and the resonance frequency in the direction
where the detecting element detects a rotational rate; and the cut-off frequency
of the low-pass filter in the circuit portion is lower than each of the synthetic
resonance-frequency and the frequency of the applied rotational rate.
