A power generating device comprising: a power generating unit configured to generate electric power by way of vibration externally applied; the power generating unit including a piezoelectric body that is deformed by the vibration to generate a voltage according to an amount of deformation, and a pair of electrodes (112, 113) disposed such that the piezoelectric body is located therebetween; an inductor electrically connected to one of the pair of electrodes and the other of the pair of electrodes, the inductor and a capacitance component of the piezoelectric body constituting a resonance circuit; a switch connected to the inductor in series; and a control circuit configured to control the switch, the control circuit having: a first control mode (driving mode) in which the control circuit controls the switch from an OFF state to an ON state in synchronism with a timing at which the voltage generated in the piezoelectric body becomes an extreme value and then controlling the switch back to the OFF state; and a second control mode, characterised in that in the second control mode (rest mode) the control circuit controls the switch to be in an OFF state regardless of the timing at which the voltage generated in the piezoelectric body becomes the extreme value, the control circuit performing the control of the second control mode after the control of the first control mode when a frequency of the vibration corresponds to a natural frequency of the power generating unit. a power generating unit configured to generate electric power by way of vibration externally applied; the power generating unit including a piezoelectric body that is deformed by the vibration to generate a voltage according to an amount of deformation, and a pair of electrodes (112, 113) disposed such that the piezoelectric body is located therebetween; a piezoelectric body that is deformed by the vibration to generate a voltage according to an amount of deformation, and a pair of electrodes (112, 113) disposed such that the piezoelectric body is located therebetween; an inductor electrically connected to one of the pair of electrodes and the other of the pair of electrodes, the inductor and a capacitance component of the piezoelectric body constituting a resonance circuit; a switch connected to the inductor in series; and a control circuit configured to control the switch, the control circuit having: a first control mode (driving mode) in which the control circuit controls the switch from an OFF state to an ON state in synchronism with a timing at which the voltage generated in the piezoelectric body becomes an extreme value and then controlling the switch back to the OFF state; and a second control mode, characterised in that in the second control mode (rest mode) the control circuit controls the switch to be in an OFF state regardless of the timing at which the voltage generated in the piezoelectric body becomes the extreme value, the control circuit performing the control of the second control mode after the control of the first control mode when a frequency of the vibration corresponds to a natural frequency of the power generating unit. a first control mode (driving mode) in which the control circuit controls the switch from an OFF state to an ON state in synchronism with a timing at which the voltage generated in the piezoelectric body becomes an extreme value and then controlling the switch back to the OFF state; and a second control mode, characterised in that in the second control mode (rest mode) the control circuit controls the switch to be in an OFF state regardless of the timing at which the voltage generated in the piezoelectric body becomes the extreme value, the control circuit performing the control of the second control mode after the control of the first control mode when a frequency of the vibration corresponds to a natural frequency of the power generating unit.