PURPOSE: To discriminate a delimiter automatically even when an interval of sent frame data differs and a personal computer receives digital data by discriminating it to be a delimiter of frame data when a reception interval of digital data for each one byte is longer than a criterion time.

CONSTITUTION: Upon the receipt of frame data Fd sent sequentially from a measurement device 1 by a personal computer 2, a CPU 6 of the personal computer 2 measures 7 data intervals of data for each byte to be sent. The mean value of the 7 measured times is compared with each of the 7 measured data. The time intervals larger than the mean value among the 7 data is a frame interval and a half of the frame intervals is set to be a criterion time. Then the CPU 6 discriminates it to be a delimiter of the frame data Fd when the reception interval of the received data is longer than the criterion time.