There is provided a displacement sensor which can precisely detect the amount of displacement given by an operator. A touch sensor which is a type of the displacement sensor has a piezoelectric element, a voltage converting unit and a detecting unit. The piezoelectric element instantaneously generates a voltage proportional to a pressing force (the amount of pressing). The voltage converting unit converts the voltage generated by the piezoelectric element, into a voltage proportional to a transition determined based on a predetermined time constant determined by an impedance of a resistor of the voltage converting unit and capacitances of a capacitor and the piezoelectric element, and a pressing force. The detecting unit integrates output voltages of the voltage converting unit, and calculates the pressing force (the amount of pressing) based on an integration value.