This is the first paper of the authors' research in dendrochronology in Japan. The work in dendrochronology is drawing-up standard charts from many wood samples collected whose falling dates have been identified. For this purpose, the authors examined the data on a cypress from Kiso Valley which was originally measured by Mr. Yamazawa in 1930. The cypress was 803 years old when it had fallen in 1920. They found characteristic years in which the four-ring-year widths along four directions on the cross-section of the wood are all broader or all narrower than those of the previous year with a probability of at least 1/8, and prepared a standard chart (M chart) indicating increase or decrease in the mean value of the four-year-ring widths compared with that of the previous year. They insist that such an M chart can be utilized to identify with at least 73% probability the age of any unknown wood sample by comparing the increase or decrease in its year-ring width with the M chart and by finding the coincidence between them.