An optical detecting device includes a receiving box and a telescopic arm. The receiving box includes an electrical connection port and a first conductive portion electrically connected to the electrical connection port. The telescopic arm is slidably disposed in the receiving box and includes an optical sensor and a second conductive portion electrically connected to the optical sensor. When the telescopic arm and the receiving box are in different sensing positions, the first conductive portion is electrically connected to the second conductive portion.