An endoscope comprising: a first wireless communication circuit unit, operably connected to a control unit, configured to transmit image data by wireless communication, the image data being in a format of transmission data in which a field number and a number showing the position in a field are included, wherein the image data pertaining to one field number constitutes one field, and characterized by a control unit configured to: - measure a total busy time of a communication channel used in the wireless communication, the total busy time being measured for the whole time period of transmitting the image data of the one field; - transmit, to an image receiving device, the image data of the one field and judge whether the transmission of the image data of the one field is complete; and - detect, upon completion of the image data transmission, a communication state of the communication channel by: -- calculating a transmission time required for transmission of image data per the one field; -- calculating a surplus time in the one field, wherein the surplus time in the one field is time available for the one field minus the transmission time required for transmission of image data per the one field; and -- judging whether a change of the communication channel is necessary based on whether the measured total busy time exceeds the calculated surplus time, wherein the wireless communication circuit unit is configured to transmit a channel change request that notifies a change of the communication channel in a case where the control unit has judged that changing the communication channel is necessary. a first wireless communication circuit unit, operably connected to a control unit, configured to transmit image data by wireless communication, the image data being in a format of transmission data in which a field number and a number showing the position in a field are included, wherein the image data pertaining to one field number constitutes one field, and characterized by a control unit configured to: - measure a total busy time of a communication channel used in the wireless communication, the total busy time being measured for the whole time period of transmitting the image data of the one field; - transmit, to an image receiving device, the image data of the one field and judge whether the transmission of the image data of the one field is complete; and - detect, upon completion of the image data transmission, a communication state of the communication channel by: -- calculating a transmission time required for transmission of image data per the one field; -- calculating a surplus time in the one field, wherein the surplus time in the one field is time available for the one field minus the transmission time required for transmission of image data per the one field; and -- judging whether a change of the communication channel is necessary based on whether the measured total busy time exceeds the calculated surplus time, wherein - measure a total busy time of a communication channel used in the wireless communication, the total busy time being measured for the whole time period of transmitting the image data of the one field; - transmit, to an image receiving device, the image data of the one field and judge whether the transmission of the image data of the one field is complete; and - detect, upon completion of the image data transmission, a communication state of the communication channel by: -- calculating a transmission time required for transmission of image data per the one field; -- calculating a surplus time in the one field, wherein the surplus time in the one field is time available for the one field minus the transmission time required for transmission of image data per the one field; and -- judging whether a change of the communication channel is necessary based on whether the measured total busy time exceeds the calculated surplus time, wherein -- calculating a transmission time required for transmission of image data per the one field; -- calculating a surplus time in the one field, wherein the surplus time in the one field is time available for the one field minus the transmission time required for transmission of image data per the one field; and -- judging whether a change of the communication channel is necessary based on whether the measured total busy time exceeds the calculated surplus time, wherein the wireless communication circuit unit is configured to transmit a channel change request that notifies a change of the communication channel in a case where the control unit has judged that changing the communication channel is necessary.