To improve the reliability in the case of transfer of data by preventing mis-conversion in the case of binary conversion when a multi-value expression is realized by voltage differences.

A conversion control section 6 continuously monitors a voltage detected by a voltage detection section 5 that detects a voltage of a multi-value signal converted into the voltage and the conversion control section 6 outputs a conversion permission signal 8 to an n-value binary conversion section 3 when the monitored voltage is kept within any voltage range corresponding to each multi-value signal value stored in a conversion table 7 for a prescribed time or over. The n-value binary conversion section 3 converts the voltage upon the receipt of the signal. According to the conversion as above, mis- conversion due to noise or the like is not cared about and the reliability at data transfer is improved.