To transmit data without raising the bit rate of a transmission line and to reduce the occurrence cause of noise.

Parallel data DATA0-DATA3 transmitted by one frame are set to be one value expressed by the array of the respective bits of parallel data. One frame is divided into a plurality of slots by the maximum value of the value expressed by the array of the respective bits of parallel data. When parallel data is four bits, for example, the slots become 16. When the value expressed by the array of the respective bits of parallel data is '1000', for example, serial data showing the eighth slot is made. Then, parallel data is converted into serial data.