To exactly detect an R wave almost real time by avoiding the erroneous detection of a peak value caused by a body motion.

In a step S1, a first amplitude value A(0) of ECG data is read and defined as a temporary maximum value MAX. In a step S2, the situation of n=n+1 is established and in a step S3, the next amplitude value A(1) of ECG data is read. Then, it is judged whether the situation of MAX-A(1)>0 is established or not. In the case of No, A(1) is defined as a temporary maximum value MAX in a step S4 and processing is returned to the step S2. In the case of Yes in the step S3, in a step S5, it is judged whether the situation of MAX-A(n)>L1 is established or not. In the case of No, processing is advanced to the step S2 and the next amplitude value A(2) of ECG data is read. Then, arithmetic in the step S3 is performed. In the case of Yes in the step S5, processing is advanced to a step S6 and the maximum value MAX is discriminated as a peak of the R wave.