PURPOSE: To obtain a spectrum trend data collecting apparatus capable of collecting a paper-making speed SPD simultaneously with spectrum data in spectrum analysis to facilitate the specification of a rotary machine having abnormality such as strain.

CONSTITUTION: This data collecting apparatus is provided with a sensor data processing part 20 to receive the measurement signals from a sensor 10 for measuring the areal weight of paper, etc., at definite frequency and perform the frequency analysis, a data collection instruction part 40 to specify the spectrum data to be collected, the tag of process data and the collection interval and a spectrum trend data collection part 50 to receive the spectrum data obtained by the frequency analysis at the sensor data processing part 20 and simultaneously receive the corresponding paper-making speed from a process controlling part 30. The roll diameter or the circumferential length of a paper machine can be determined from the corresponding paper-making speed and the peak frequency value in the spectrum data displayed on a spectrum trend data displaying part 70.