This paper aims to identify the planning method of the inner citadel of the Japanese castle, Echizen Fukui castle in the age of civil wars, about A.D. 1600. The conclusions are as follows, 1. The planning of the inner citadel in the age of civil wars was carried out owing to the precise drawings by the geometrical method. 2. The principal planning methods for the planning were the right angled triangle by Pyhthagoras's number (3:4:5), the magic square and the perpendicular.