A management device being configured to transmit data to a plurality of terminal devices by way of communication relay devices on a connected communication network and to control the plurality of terminal devices, the management device comprising: a transmission data storage section being configured to store transmission data; a group information storage section being configured to store group information on groups to which each of the plurality of terminal devices belongs and information on a communication time frame of one or more terminal devices for each group; and a first communication control section (120a, 120h) being configured to control communication with the plurality of terminal devices based on the group information and the information on the communication time frame, wherein the first communication control section is configured to issue a start notification of data transmission of firmware for update and an extension request for extending an operating time at a next activation in one-to-one communication to each terminal device belonging to a group in a transmissible state of the groups, the start notification being for putting the each terminal device into a state where the each terminal device receives the transmission data from the management device and starts to update a reception status of the transmission data, and to store a terminal device that has responded to the start notification, to start, regardless of whether each terminal device has responded to the start notification or not, transmission of the transmission data in one-to-multiple communication to each terminal device belonging to a group in the transmissible state of the groups after the start notification, and to issue, after completion of the transmission of the transmission data, a transmission request of the reception status of the transmission data in one-to-one communication to the terminal device that has responded to the start notification and belongs to a group in the transmissible state of the groups. a transmission data storage section being configured to store transmission data; a group information storage section being configured to store group information on groups to which each of the plurality of terminal devices belongs and information on a communication time frame of one or more terminal devices for each group; and a first communication control section (120a, 120h) being configured to control communication with the plurality of terminal devices based on the group information and the information on the communication time frame, wherein the first communication control section is configured to issue a start notification of data transmission of firmware for update and an extension request for extending an operating time at a next activation in one-to-one communication to each terminal device belonging to a group in a transmissible state of the groups, the start notification being for putting the each terminal device into a state where the each terminal device receives the transmission data from the management device and starts to update a reception status of the transmission data, and to store a terminal device that has responded to the start notification, to start, regardless of whether each terminal device has responded to the start notification or not, transmission of the transmission data in one-to-multiple communication to each terminal device belonging to a group in the transmissible state of the groups after the start notification, and to issue, after completion of the transmission of the transmission data, a transmission request of the reception status of the transmission data in one-to-one communication to the terminal device that has responded to the start notification and belongs to a group in the transmissible state of the groups.