An image data decoding apparatus and method are based on an availability of reference data. The image data decoding apparatus may include a core to process decoding of image data, and an availability determining device to receive, from the core, availability verification request information with respect to a reference area of a first frame included in the image data, to determine an availability with respect to the reference area based on the received availability verification request information, and to transmit, to the core, the determined availability. When the reference area is available, the core may process decoding of a second frame based on the reference area.