An image encoding/decoding apparatus is provided, including a frequency band division unit for dividing image data into a plurality of frequency bands to generate sub-band coefficients, a sub-band coefficient interpolation unit for interpolating sub-band coefficients outside a region of a shape by using shape information representing a shape of the image data and the sub-band coefficients in the region of the shape, an encoding unit for encoding the interpolated sub-band coefficients to generate encoded data, and a shape information encoding unit for encoding the shape information to generate shape information encoded data.