To provide a resonant zone widening circuit which widens the effective resonant zone of a self-exciting oscillation circuit and, at the same time, reflects the impedance characteristic of a piezoelectric oscillator and a tactile sensor which detects the visco-elasticity characteristic of an object by using the widening circuit.

The resonant zone widening circuit is installed to the self-exciting oscillation circuit, which is connected to the piezoelectric oscillator and oscillates the oscillator by feeding back the impedance characteristic of the oscillator to the oscillator by using the equivalent circuit constant of the oscillator as a circuit element, and manifests a plurality of resonance modes together with the equivalent circuit of the oscillator. The tactile sensor has the piezoelectric oscillator, the self-oscillation circuit which is connected to the oscillator and oscillates the oscillator by feeding back the impedance characteristic to the oscillator by using the equivalent circuit constant of the oscillator as the circuit element, and the resonant zone widening circuit which manifests the resonance modes together with the equivalent circuit of the oscillator installed to the oscillation circuit and widens the effective resonance frequency of the oscillator of the oscillation circuit by means of the widening circuit.