A self-oscillation circuit (100, 200, 300, 400) comprising: a positive feedback circuit including: a vibration unit having a vibrator; an inverting amplifier configured to invert and amplify a signal output from the vibration unit; and a switch circuit, wherein a positive feedback path is configured by a path that extends from an output of the inverting amplifier to an input of the vibration unit via the switch circuit, the positive feedback path positively feeding back a signal based on vibration of the vibrator to the vibration unit; and a negative feedback circuit configured to receive the inverted and amplified signal output from the inverting amplifier and to generate a pulse-width-modulated signal having a frequency lower than a vibration frequency of the vibrator, based on a comparison result between a value corresponding to an amplitude of the vibrator and a reference value, the value corresponding to the amplitude of the vibrator being based on the inverted and amplified signal output from the inverting amplifier, wherein the switch circuit is configured to be switched by the pulse-width-modulated signal between a state in which the inverted and amplified signal output from the inverting amplifier is fed back to the vibration unit to form the positive feedback path of the positive feedback circuit and a state in which the positive feedback path of the positive feedback circuit is released. a positive feedback circuit including: a vibration unit having a vibrator; an inverting amplifier configured to invert and amplify a signal output from the vibration unit; and a switch circuit, wherein a positive feedback path is configured by a path that extends from an output of the inverting amplifier to an input of the vibration unit via the switch circuit, the positive feedback path positively feeding back a signal based on vibration of the vibrator to the vibration unit; and a vibration unit having a vibrator; an inverting amplifier configured to invert and amplify a signal output from the vibration unit; and a switch circuit, wherein a positive feedback path is configured by a path that extends from an output of the inverting amplifier to an input of the vibration unit via the switch circuit, the positive feedback path positively feeding back a signal based on vibration of the vibrator to the vibration unit; and a negative feedback circuit configured to receive the inverted and amplified signal output from the inverting amplifier and to generate a pulse-width-modulated signal having a frequency lower than a vibration frequency of the vibrator, based on a comparison result between a value corresponding to an amplitude of the vibrator and a reference value, the value corresponding to the amplitude of the vibrator being based on the inverted and amplified signal output from the inverting amplifier, wherein the switch circuit is configured to be switched by the pulse-width-modulated signal between a state in which the inverted and amplified signal output from the inverting amplifier is fed back to the vibration unit to form the positive feedback path of the positive feedback circuit and a state in which the positive feedback path of the positive feedback circuit is released.