More suitable image encoding technique and image decoding technique are provided. An image encoding method for encoding an image includes: a predicted image generation step of generating a predicted image of a synthesis prediction by performing synthesis processing of synthesizing a predicted image of an inter prediction and a predicted image of an intra prediction to an encoding-target block; and an encoding step of encoding a difference between the predicted image generated in the predicted image generation step and a pixel value of an image of the encoding-target block, the synthesizing processing includes weighting processing performed to the predicted image of the inter prediction and the predicted image of the intra prediction, and a weighting parameter of the weighting processing is determined in accordance with a type of the intra prediction.