An image signal processing device includes: a base component extractor that generates an original base component signal; a base component adjuster that generates a first base component signal by performing weighted average processing; a detail component extractor that generates a first detail component signal based on the first base component signal; a relative emphasizer that outputs a second base component signal and a second detail component signal by relatively emphasizing the first detail component signal to the first base component signal; a combiner that generates a combined image signal by combining the second base component signal and the second detail component signal; and a storage that stores control parameters regarding similarity between the image signal and the first base component signal. The base component adjuster generates the first base component signal by performing the weighted average processing by using a weight coefficient determined in accordance with selected control parameter.