To provide a biphase coded data decoding method.

A biphase coded data decoding method of the present invention works in such a way that falling edge conversions in biphase coded data are detected, and based on a time difference value between two adjacent falling edge conversions and a logic value of preceding one bit, suitable decoding is performed. When the time difference value is a 1 bit period and the preceding one bit is a logic 1, the current bit is determined to be a logic 1; when the time difference value is a 1 bit period and the preceding one bit is a logic 0, the current bit is determined to be a logic 0; when the time difference value is a 1.5 bit period and the preceding one bit is a logic 1, the current bit and following one bit are both logic 0s; when the time difference value is a 1.5 bit period and the preceding one bit is a logic 0, the current bit is determined to be a logic 1; when the time difference value is a 2 bit period and the preceding one bit is a logic 1, the current bit and following one bit respectively are determined to be a logic 0 and logic 1.