A serial data transmission device (100a; 100b; 100c) comprising: a receiver (110a; 110b; 110c) that is configured to receive first data allocated in a predetermined number of time slots (LOAD_SLOT_SIZE) during a frame transmission period, the time slots are serially transmitted by a time-division multiplex method with a predetermined receiving-side repetition period from a first device (100a; 100b; 100c) daisy-chained to the serial data transmission device (100a; 100b; 100c); wherein the time slots in the time-division multiplex method have a specific size and are transmitted in sequence, and wherein the frame transmission period is a predetermined constant period, a controller (145a, 150a; 145b, 150b; 145c, 150c) that is configured to determine a second number of time slots (LOAD_SLOT_SIZE) required for a second data to be transmitted by a time-division multiplex method with a predetermined transmitting-side repetition period the serial data transmission device (100a; 100b; 100c) to a second device (100a; 100b; 100c), and is further configured to uniquely allocate the second data into the determined second number of time slots (LOAD_SLOT_SIZE), and is further configured to maintain the signal allocation of the first data, and further comprising a clock adjusting circuit (160, 170) that is configured to increase a transmitting-side clock speed only in a case where the transmitting-side repetition period of the time slots to be time-division multiplexed is longer than the receiving-side repetition period, and further comprising a transmitter (140a; 140b; 140c) configured to serially transmit the second data and the first data by the time-division multiplex method with the predetermined transmitting-side repetition period to a second device (100a; 100b; 100c) daisy-chained to the serial data transmission device (100a; 100b; 100c). a receiver (110a; 110b; 110c) that is configured to receive first data allocated in a predetermined number of time slots (LOAD_SLOT_SIZE) during a frame transmission period, the time slots are serially transmitted by a time-division multiplex method with a predetermined receiving-side repetition period from a first device (100a; 100b; 100c) daisy-chained to the serial data transmission device (100a; 100b; 100c); wherein the time slots in the time-division multiplex method have a specific size and are transmitted in sequence, and wherein the frame transmission period is a predetermined constant period, a controller (145a, 150a; 145b, 150b; 145c, 150c) that is configured to determine a second number of time slots (LOAD_SLOT_SIZE) required for a second data to be transmitted by a time-division multiplex method with a predetermined transmitting-side repetition period the serial data transmission device (100a; 100b; 100c) to a second device (100a; 100b; 100c), and is further configured to uniquely allocate the second data into the determined second number of time slots (LOAD_SLOT_SIZE), and is further configured to maintain the signal allocation of the first data, and further comprising a clock adjusting circuit (160, 170) that is configured to increase a transmitting-side clock speed only in a case where the transmitting-side repetition period of the time slots to be time-division multiplexed is longer than the receiving-side repetition period, and