In the data transmission system 1 for transmitting drive pulse data from a personal computer to an ink jet printer in 8-bit units, the drive pulse data includes 7 bits of pulse width data Hx and 9 bits of pulse interval data Lx. The personal computer reduces pulse interval data, which has an amount of data exceeding 8 bits, in half by shifting the bits one place to the right before transmitting the data to the inkjet printer. The basic time period used for decoding the pulse interval data is set to twice the basic time period used for decoding the pulse width data. The pulse interval data is decoded based on this larger basic time period.