1. An image processor comprising: an image inputting means for inputting as an image signal an image of an area adjacent to a vehicle from a camera provided for the vehicle; a mask information storing means for storing mask information, which is information on a mask; a mask processing executing means for carrying out mask processing on the image inputted by the image inputting means based on the mask information stored in the mask information storing means; and an outputting means for outputting an image subjected to mask processing by the mask processing executing means to a display device, wherein a shape of the image outputted to the display device by the outputting means is substantially rectangular, wherein a mask represented by the mask information stored in the mask information storing means includes an upper mask and a lower mask, the upper mask being concave on a lower side thereof and being disposed along an upper side of the image when the image is displayed in the display device, the lower mask being concave on an upper side thereof and being disposed along a lower side of the image when the image is displayed in the display device.