Major damage was found in a group of trees growing in an elliptically shaped area of approximately 40 m internal in a 58-year-old artificial forest of Japanese cypress in Ibaraki Prefecture. From the sudden and simultaneous occurrence of the damage, the cause was determined to be lightning strike. Other possible causes investigated were all ruled out. The first manifestation of lightning damage to the group appeared as leaf blight in April of the following year of the lightning occurrence. The damage did not expand to trees outside of this 40 m diameter range for three years. However, inside the range, some trees that had shown dieback or partial crown wilting when the lightning damage first appeared, eventually died with their whole crown wilted. The progress of crown wilting was supposed to be caused by wood borer. The condition of damage to a group of trees in a Japanese cypress forest by lightning in this case agreed well with descriptions in previous reports of lightning damage in Japanese cedar and Japanese red pine forests. The date and location of the lightning were verified by the meteorological data.