A digital key system comprising: a digital key; a digital lock to be locked and unlocked with the digital key; and a controller configured to control the digital lock, wherein the digital key includes a battery, a non-contact memory storing unlocking authority information corresponding to information of an authority needed to unlock the digital lock and an electromagnetic induction coil configured to read information from the non-contact memory in a non-contact manner, the controller includes: a near field communication unit configured to perform communication with the digital key; and a microcomputer configured to control the near field communication unit, the digital key and the digital lock each include two terminals (21, 22, 41, 42) and are configured to provide an electric circuit when the digital key and the digital lock are connected to each other through the respective two terminals, the electric circuit being configured to superimpose and separate a high-frequency signal and a DC current, and when the microcomputer starts operating upon receiving the DC current supplied from the battery through the electric circuit when the digital key is connected with the digital lock, the microcomputer being configured to cause the near field communication unit to perform communication by the high-frequency signal with the electromagnetic induction coil of the digital key through the electric circuit to read the unlocking authority information from the non-contact memory, and authenticate the read unlocking authority information, the digital key system further includes a connection part in which the two terminals (21, 22) of the digital key and the two terminals (41, 42) of the digital lock are connected to each other, the connection part being configured to superimpose the DC current and the high-frequency signal to mutually supply power between the digital key and the digital lock, and wherein the electric circuit is configured to superimpose the DC current from the battery of the digital key and the high-frequency signal transmitted from the non-contact memory via the electromagnetic induction coil, and transmit the superimposed signal from the digital key to the digital lock, and then separate the superimposed signal into the DC current and the high-frequency signal and transmit the DC current and the high-frequency signal respectively to the microcomputer and the near field communication unit. a digital key; a digital lock to be locked and unlocked with the digital key; and a controller configured to control the digital lock, wherein the digital key includes a battery, a non-contact memory storing unlocking authority information corresponding to information of an authority needed to unlock the digital lock and an electromagnetic induction coil configured to read information from the non-contact memory in a non-contact manner, the controller includes: a near field communication unit configured to perform communication with the digital key; and a microcomputer configured to control the near field communication unit, a near field communication unit configured to perform communication with the digital key; and a microcomputer configured to control the near field communication unit, the digital key and the digital lock each include two terminals (21, 22, 41, 42) and are configured to provide an electric circuit when the digital key and the digital lock are connected to each other through the respective two terminals, the electric circuit being configured to superimpose and separate a high-frequency signal and a DC current, and when the microcomputer starts operating upon receiving the DC current supplied from the battery through the electric circuit when the digital key is connected with the digital lock, the microcomputer being configured to cause the near field communication unit to perform communication by the high-frequency signal with the electromagnetic induction coil of the digital key through the electric circuit to read the unlocking authority information from the non-contact memory, and authenticate the read unlocking authority information, the digital key system further includes a connection part in which the two terminals (21, 22) of the digital key and the two terminals (41, 42) of the digital lock are connected to each other, the connection part being configured to superimpose the DC current and the high-frequency signal to mutually supply power between the digital key and the digital lock, and wherein the electric circuit is configured to superimpose the DC current from the battery of the digital key and the high-frequency signal transmitted from the non-contact memory via the electromagnetic induction coil, and transmit the superimposed signal from the digital key to the digital lock, and then separate the superimposed signal into the DC current and the high-frequency signal and transmit the DC current and the high-frequency signal respectively to the microcomputer and the near field communication unit.