Abstract: An apparatus for measuring the distance of a target includes a circuit arrangement of a transmitting circuit, a first receiving circuit, a second receiving circuit, a charging/discharging circuit, a switching gate, an analog-to-digital converter, a microprocessor, and a monitor. A modulated pulse signal is emitted by the transmitting circuit, and will be received by the first receiving circuit which makes the charging/discharging circuit start being charged. When the modulated pulse signal is reflected from a reflective object, it will be received by the second receiving circuit and the second receiving circuit will send a stop signal to terminate the charge to the capacitor of the charging/discharging circuit. By calculating the time period of the charging time under the control of switching gate, analog-to-digital converter, microprocessor, the distance of a target object is measured.