To improve the reliability of correlation of each sensitivity characteris tic checking device by calculating the correlation of the power output value between each sensitivity characteristic checking device from the recording sensitivity characteristic graph of the same recording medium obtained with the measurement by each sensitivity checking device.

The name of the sensitivity characteristic checking device for obtaining correlation is designated as a device α and device β, and the name of a recording medium to be used is designated as a medium γ. An approximate repression (two dimensional and multionominal approximate expression) wherein the output value of the device β is converted into the power output of the device α is shown by a graph. In the graph, values x1α, x2α, x3α,... and x1β, x1β, x2β, x3β,... of the applying power corresponding to values y1, y2, y3,... of a recording signel quantity are respectively plotted on a vertical axis and horizontal axis as a measuring point. The obtained conversion equation is as follows. y=0.0041x2+0.928x (R-2 square value R2=0.9993). However, the output in the device α is meant by (y) and the power output in the device β is meant by (x).