A camera apparatus, comprising: a camera unit disposed in a first area (El) separated from a second area by an obstacle, the camera unit including a camera module configured to capture an image of part of the first area (El); a relay unit disposed in the second area, the relay unit having a function of transmitting the image captured by the camera unit to a first device in the second area by wireless communication; and a connector which electrically connects the camera unit to the relay unit, the camera unit further including a communicator configured to perform wireless communication with a second device which is disposed in the first area and is configured to perform monitoring in the first area, the relay unit further having a function of transmitting, to the first device, a monitoring result by the second device which is transmitted from the second device and received by the communicator, characterized in that: when the relay unit receives a signal containing the monitoring result transmitted by the second device, the relay unit is configured to determine whether or not another signal is being transmitted to the first device; and if the relay unit determines that another signal is not being transmitted, the relay unit is configured to transmit the monitoring result to the first device; and if the relay unit determines that another signal is being transmitted, i) the relay unit is configured to discard the signal received and to request the second device to transmit a signal again, or ii) the relay unit is configured to hold the signal received until the transmission of the another signal is finished, and when the transmission of the another signal is finished, the relay unit is configured to transmit the signal held. a camera unit disposed in a first area (El) separated from a second area by an obstacle, the camera unit including a camera module configured to capture an image of part of the first area (El); a relay unit disposed in the second area, the relay unit having a function of transmitting the image captured by the camera unit to a first device in the second area by wireless communication; and a connector which electrically connects the camera unit to the relay unit, the camera unit further including a communicator configured to perform wireless communication with a second device which is disposed in the first area and is configured to perform monitoring in the first area, the relay unit further having a function of transmitting, to the first device, a monitoring result by the second device which is transmitted from the second device and received by the communicator, characterized in that: when the relay unit receives a signal containing the monitoring result transmitted by the second device, the relay unit is configured to determine whether or not another signal is being transmitted to the first device; and if the relay unit determines that another signal is not being transmitted, the relay unit is configured to transmit the monitoring result to the first device; and if the relay unit determines that another signal is being transmitted, i) the relay unit is configured to discard the signal received and to request the second device to transmit a signal again, or ii) the relay unit is configured to hold the signal received until the transmission of the another signal is finished, and when the transmission of the another signal is finished, the relay unit is configured to transmit the signal held. when the relay unit receives a signal containing the monitoring result transmitted by the second device, the relay unit is configured to determine whether or not another signal is being transmitted to the first device; and if the relay unit determines that another signal is not being transmitted, the relay unit is configured to transmit the monitoring result to the first device; and if the relay unit determines that another signal is being transmitted, i) the relay unit is configured to discard the signal received and to request the second device to transmit a signal again, or ii) the relay unit is configured to hold the signal received until the transmission of the another signal is finished, and when the transmission of the another signal is finished, the relay unit is configured to transmit the signal held. i) the relay unit is configured to discard the signal received and to request the second device to transmit a signal again, or ii) the relay unit is configured to hold the signal received until the transmission of the another signal is finished, and when the transmission of the another signal is finished, the relay unit is configured to transmit the signal held.