To enable mapping of a texture on a surface of an object projected even if the object projected changes its shape, moves or the like.

The image processing device 4 of an apparatus 1 used for projection mapping comprises a computer 40 that repeatedly executes: image inputting processing for inputting images including an image of an object projected 99 taken by an electronic camera 43; coordinate conversion processing for coordinate-converting an image 70 inputted by the image input process from a coordinate system of the electronic camera 43 to a coordinate system of a display screen; region extraction processing for extracting a closed region 73a of the image 73 of the object projected 99 of images 72 converted by the coordinate conversion processing; mapping processing for mapping an object 41b on the closed region 73a extracted by the region extraction processing; and picture-signal generation processing for generating a picture signal of the display screen including the object 41b mapped by the mapping processing.