A data transmission device (21, 121, 221, 321), comprising: a communicator connected to a network (31, 32, 33), the communicator performing a communication with another device (22, 51, 61)via the network (31, 32, 33); and a controller transmitting, from the communicator to the other device (22, 51, 61), a data set including data of at least one item, characterized in that the controller is configured to perform the following steps: acquiring (S101, S111) the data of the at least one item at a first interval, determining (S103, S113) whether or not one interval of a second interval has elapsed according to the acquiring the data of the at least one item, the second interval being slower than the first interval, updating (S104, S114) the data of the at least one item when the one interval of the second interval has elapsed, determining (S105, S115) whether or not the data of the at least one item included in the data set including the data after the updating has changed from the update of the previous time, transmitting (S106, S116) the data set to the other device (22, 51, 61) at a second interval or at a frequency less than the second interval by transmitting the data set including the data after the updating from the communicator to the other device (22, 51, 61) when the data of the at least one item included in the data set has changed from the update of the previous time, determining whether or not a retransmission time has elapsed in a first case (S105, S107, S115, S117) and a second case (S103, S107, S113, S117), the first case being a case that there is no change in the data of the at least one item included in the data set from the update of the previous time, the second case being a case that the one interval of the second interval has not elapsed, transmitting the data set from the communicator to the other device (22, 51, 61) when the retransmission time has elapsed (S106, S107, S116, S117), and performing no transmission of the data set when the retransmission time has not elapsed. a communicator connected to a network (31, 32, 33), the communicator performing a communication with another device (22, 51, 61)via the network (31, 32, 33); and a controller transmitting, from the communicator to the other device (22, 51, 61), a data set including data of at least one item, characterized in that the controller is configured to perform the following steps: acquiring (S101, S111) the data of the at least one item at a first interval, determining (S103, S113) whether or not one interval of a second interval has elapsed according to the acquiring the data of the at least one item, the second interval being slower than the first interval, updating (S104, S114) the data of the at least one item when the one interval of the second interval has elapsed, determining (S105, S115) whether or not the data of the at least one item included in the data set including the data after the updating has changed from the update of the previous time, transmitting (S106, S116) the data set to the other device (22, 51, 61) at a second interval or at a frequency less than the second interval by transmitting the data set including the data after the updating from the communicator to the other device (22, 51, 61) when the data of the at least one item included in the data set has changed from the update of the previous time, determining whether or not a retransmission time has elapsed in a first case (S105, S107, S115, S117) and a second case (S103, S107, S113, S117), the first case being a case that there is no change in the data of the at least one item included in the data set from the update of the previous time, the second case being a case that the one interval of the second interval has not elapsed, transmitting the data set from the communicator to the other device (22, 51, 61) when the retransmission time has elapsed (S106, S107, S116, S117), and performing no transmission of the data set when the retransmission time has not elapsed. acquiring (S101, S111) the data of the at least one item at a first interval, determining (S103, S113) whether or not one interval of a second interval has elapsed according to the acquiring the data of the at least one item, the second interval being slower than the first interval, updating (S104, S114) the data of the at least one item when the one interval of the second interval has elapsed, determining (S105, S115) whether or not the data of the at least one item included in the data set including the data after the updating has changed from the update of the previous time, transmitting (S106, S116) the data set to the other device (22, 51, 61) at a second interval or at a frequency less than the second interval by transmitting the data set including the data after the updating from the communicator to the other device (22, 51, 61) when the data of the at least one item included in the data set has changed from the update of the previous time, determining whether or not a retransmission time has elapsed in a first case (S105, S107, S115, S117) and a second case (S103, S107, S113, S117), the first case being a case that there is no change in the data of the at least one item included in the data set from the update of the previous time, the second case being a case that the one interval of the second interval has not elapsed, transmitting the data set from the communicator to the other device (22, 51, 61) when the retransmission time has elapsed (S106, S107, S116, S117), and performing no transmission of the data set when the retransmission time has not elapsed.