PURPOSE: To enable drying unseasoned wood in the form of a log to be conducted fast without involving warping, cracking, deepening in shade, or the like by finding the moisture content of unseasoned wood from an image of a cut end thereof through selection of a sample image being a closest approximation in denseness of the annual rings and shade of color.

CONSTITUTION: A camera part 20 photographs both two cut ends of unseasoned timber which has been brought from a timber yard 2 and the image data obtained are sent to a preprocessing part 4. Next the unseasoned timber is taken to a preprocessing apparatus 3 where a conical hollow is formed in each of the cut ends and a preprocessing device 4 measures the length L, diameter D, and weight W and finds the volume V and density P. On the other hand, out of image data sent from the camera part and stored in memory in a large number in a data-processing device data on sample image which is a closest approximation in denseness of annual rings and shade of color is selected. Then on the basis of the density P and the density after drying belonging to the data on sample image the moisture content of the unseasoned timber is specified; from the moisture content various details of the condition suitable for microwave heating are determined. Then the timber is subjected to primary drying by exposure to microwave radiation.