The impulse response represents the transmission characteristics from the certain source point to the receiving point of the room, if we consider it to be a linear system. According to the position of the source and receiving points some differences are caused in the impulse responses, but they imply the spatial characteristics of the room. The mirror image method is often used to obtain the spatial characteristics of a room, but it is difficult to apply this method to an actual room because of the complexity of the room shape. At four slightly variant receiving points onx,y, andzaxis, we measured the impulse responses of the same source point. Then we computed the image sources to the three dimensional field. From these virtual image sources, we obtained SPL distributions, conditions of standing waves, effects of absorbing materials, mean free path, etc., in a room.