A communication device, comprising a main unit that includes a communication unit and is configured to be supplied with electric power from a battery to be activated, and an operation unit, wherein the communication device further comprises a processing unit that is configured to cause the main unit to operate in an operation mode as any one of a first operation mode for performing a normal operation and a second operation mode for performing a stand-by operation, power consumption in which is smaller than that in the first operation mode, a first determining unit that is configured to, when the operation mode is the second operation mode, determine whether or not the operation unit receives a changeover instruction to the first operation mode, and a second determining unit that is configured to, when the first determining unit determines receipt of the changeover instruction, determine whether or not a changeover condition of the operation mode from the second operation mode to the first operation mode is fulfilled, wherein the processing unit is configured to, when the second determining unit determines fulfilment of the changeover condition, change the operation mode from the second operation mode to the first operation mode, wherein the communication device is characterized in that the main unit comprises an installation detector that is configured to detect installation of an enclosure accommodating at least the main unit and the processing unit, the processing unit is configured to cause the installation detector to operate in an installation detection enabled state when the first determining unit determines the receipt of the changeover instruction by the operation unit, the second determining unit is configured to determine the fulfilment of the changeover condition when the installation detector detects the installation of the enclosure (lOB) within a predetermined time period beginning at start of operation of the installation detector in the installation detection enabled state, and determine unfulfilment of the changeover condition when the installation detector does not detect the installation of the enclosure (lOB) within the predetermined time period, and the processing unit is configured to deactivate the installation detector when the second determining unit determines the unfulfilment of the changeover condition. a processing unit that is configured to cause the main unit to operate in an operation mode as any one of a first operation mode for performing a normal operation and a second operation mode for performing a stand-by operation, power consumption in which is smaller than that in the first operation mode, a first determining unit that is configured to, when the operation mode is the second operation mode, determine whether or not the operation unit receives a changeover instruction to the first operation mode, and a second determining unit that is configured to, when the first determining unit determines receipt of the changeover instruction, determine whether or not a changeover condition of the operation mode from the second operation mode to the first operation mode is fulfilled, wherein the processing unit is configured to, when the second determining unit determines fulfilment of the changeover condition, change the operation mode from the second operation mode to the first operation mode, wherein the communication device is characterized in that the main unit comprises an installation detector that is configured to detect installation of an enclosure accommodating at least the main unit and the processing unit, the processing unit is configured to cause the installation detector to operate in an installation detection enabled state when the first determining unit determines the receipt of the changeover instruction by the operation unit, the second determining unit is configured to determine the fulfilment of the changeover condition when the installation detector detects the installation of the enclosure (lOB) within a predetermined time period beginning at start of operation of the installation detector in the installation detection enabled state, and determine unfulfilment of the changeover condition when the installation detector does not detect the installation of the enclosure (lOB) within the predetermined time period, and determine the fulfilment of the changeover condition when the installation detector detects the installation of the enclosure (lOB) within a predetermined time period beginning at start of operation of the installation detector in the installation detection enabled state, and determine unfulfilment of the changeover condition when the installation detector does not detect the installation of the enclosure (lOB) within the predetermined time period, and the processing unit is configured to deactivate the installation detector when the second determining unit determines the unfulfilment of the changeover condition.