When a quantized DCT coefficient and a quantization parameter are input from an entropy decoder, a controller outputs them to a switch and gives a load detector an instruction to detect system load. The load detector requests system load information from OS. If the system load is light, the load detector controls the switch to execute first inverse quantization of general load by a general processor and obtain a DCT coefficient. If the system load is heavy, the load detector controls the switch to execute second inverse quantization whose processing load is lighter than the first inverse quantization by a specific processor and obtain a DCT coefficient.