This paper presents an automatic 3D furniture placement system for 3D virtual room generation. The layout work for 3D virtual room takes a long time because 3D objects have six degrees of freedom and furniture has peculiar features. To deal with this problem, the authors present an automatic optimization method by using interactive evolutionary computation. Furniture layouts are optimized through the use of prior information stored in a semantic database and the user preference. This paper mainly introduces the way of construction of gene expression and evolution process for interactive evolutionary computation. Optimization process is performed based on the minimization of cost function and maximization of user satisfaction. During this optimization, user can make an adjustment as necessary. In this paper, the authors introduce the prototype system and discuss its usefulness.