A control unit arranged to control a movement of a reflector, comprising: a drive signal output unit arranged to apply a cyclical drive voltage having a first minimum value and a maximum value in one cycle to a piezoelectric element so as to deform the piezoelectric element, wherein the deformation of the piezoelectric element causes the reflector to move; and a controller arranged to control the drive voltage to have the first minimum value greater than a zero voltage by a given difference value, such that the given difference value is the voltage difference between the zero voltage and the first minimum value; characterised in that the difference value is set such that a change rate of a piezoelectric constant value of the piezoelectric element in the one cycle of the drive voltage having the first minimum value greater than the zero voltage by the given difference value becomes smaller than a change rate of the piezoelectric constant value of the piezoelectric element in the one cycle of the drive voltage having the minimum value of zero voltage; wherein the given difference value is set such that the change rate of the piezoelectric constant value of the piezoelectric element in the one cycle of the drive voltage becomes within 20%; wherein the drive voltage substantially is a sawtooth wave such that a rising time of the drive voltage is different from a falling time of the drive voltage; and wherein the piezoelectric element includes a first piezoelectric element and a second piezoelectric element; and the drive signal output unit is arranged to apply a first drive voltage having a first sawtooth waveform to the first piezoelectric element, and a second drive voltage having a second sawtooth waveform to the second piezoelectric element, and the controller is arranged to set the first minimum value of the first drive voltage having the first sawtooth waveform differently from a second minimum value of the second drive voltage having the second sawtooth waveform such that the constantness of the movement speed of the reflector is further enhanced. a drive signal output unit arranged to apply a cyclical drive voltage having a first minimum value and a maximum value in one cycle to a piezoelectric element so as to deform the piezoelectric element, wherein the deformation of the piezoelectric element causes the reflector to move; and a controller arranged to control the drive voltage to have the first minimum value greater than a zero voltage by a given difference value, such that the given difference value is the voltage difference between the zero voltage and the first minimum value; characterised in that the difference value is set such that a change rate of a piezoelectric constant value of the piezoelectric element in the one cycle of the drive voltage having the first minimum value greater than the zero voltage by the given difference value becomes smaller than a change rate of the piezoelectric constant value of the piezoelectric element in the one cycle of the drive voltage having the minimum value of zero voltage; wherein the given difference value is set such that the change rate of the piezoelectric constant value of the piezoelectric element in the one cycle of the drive voltage becomes within 20%; wherein the drive voltage substantially is a sawtooth wave such that a rising time of the drive voltage is different from a falling time of the drive voltage; and wherein the piezoelectric element includes a first piezoelectric element and a second piezoelectric element; and the drive signal output unit is arranged to apply a first drive voltage having a first sawtooth waveform to the first piezoelectric element, and a second drive voltage having a second sawtooth waveform to the second piezoelectric element, and the controller is arranged to set the first minimum value of the first drive voltage having the first sawtooth waveform differently from a second minimum value of the second drive voltage having the second sawtooth waveform such that the constantness of the movement speed of the reflector is further enhanced.