A telephone device includes a base, a light transmitter, a light penetrating element for penetrating light transmitter from the light transmitter, and a handset. When an end of the handset is on-hook with the base, the end of the handset reflects the light emitted from the light transmitter and penetrating through the light penetrating element back to the light penetrating element. The telephone device further includes a light receiver for receiving the light reflected from the handset when the end of the handset is on-hook with the base, a light concentrating element for concentrating the light emitted from the light transmitter to the light penetrating element, and a control unit for determining whether the end of the handset is on-hook with the base according to whether the light receiver receives the light reflected from the handset.