A communication system includes a variable device, which is one of a management device and a terminal device, having a power determination unit and a transmission instruction unit. State information indicates a state of a housing that houses the communication system. A power determination unit is configured to determine a transmission power value as an applicable power value for a transmission of a wireless communication signal to a target device to achieve a predetermined communication quality when the state of the housing has changed based on the state information. The target device, which is the other of the management device and the terminal device, is a device with which the variable device communicates. A transmission instruction unit instructs a wireless communication device in the variable device to transmit the wireless communication signal to the target device at the applicable power value.