A filtering method is for performing deblocking filtering on the boundary between an IPCM block and a non-IPCM block adjacent to each other in an image and including: determining a first quantization parameter for the non-IPCM block; determining a second quantization parameter for the IPCM block, using the first quantization parameter; determining a filter strength for the boundary, using the first quantization parameter and the second quantization parameter; and performing the deblocking filtering on the boundary using the determined filter strength.