An image coding method for coding an input image per block to generate a coded image signal includes: predicting for each prediction unit which is an area obtained by partitioning a target block to generate a prediction image of the target block; comparing a transform unit which is an area obtained by partitioning the target block and is a processing unit for frequency transform with the prediction unit, to detect part of a boundary of the prediction unit, the boundary being located within the transform unit; performing boundary filtering on the detected part of the boundary in the generated prediction image; calculating a difference between a filtered prediction image and the input image to generate a difference image of the target block; and performing frequency transform on the difference image for each transform unit.