In a single-wire data communication characterized in that a data communication unit time is different in accordance with the polarity of a signal, a communication control time is dependent on a communication data pattern, and hence, the control of the whole system is difficult. A counter for counting a clock continues the counting until a count value thereby obtained reaches a predetermined upper limit value, retains the predetermined upper limit value as the count value until a next pulse is detected in a reception signal after the count value reaches the predetermined upper limit value, and initializes the count value when the next pulse is detected. A data value judger judges a data value depending on whether or not the pulse is detected during a period before the time when the count value reaches the predetermined upper limit value.