There is a well-known problem that it is very difficult to accurately make a 3D object move/rotate to a specific position/orientation in a virtual 3D space by the direct manipulation of a mouse device on a 2D computer display screen. To deal with this problem, the authors have already proposed an automatic 3D object layout method based on contact constraints. After automatically generating a 3D scene using this method, the user often wants to modify it manually. For this, the authors propose voice commands for 3D object layout based on contact constraints in this paper. With the contact constraints used in the 3D object layout method, it becomes easier to layout 3D objects by voice commands. Voice commands are intuitive interface and very efficient in the situation when the user can not use a mouse device.