An image processing apparatus comprises an acquisition unit that acquires images of a plurality of continuous frames obtained by shooting a subject; and a synthesis unit which generates a second image by performing lighten composite on first images of a plurality of continuous frames acquired with a first exposure amount out of the plurality of frames of images, acquires a fourth image by performing gain processing on a third image acquired with a second exposure amount which is lower than the first exposure amount so that the fourth image has a same exposure level as the first images, and generates a composite image showing a trail of the subject by performing lighten composite on a difference image, obtained by subtracting the fourth image from the second image, and the third image.