A CIS-based thin film solar cell has a backside electrode layer that is divided by a pattern (P1), and a CIS-based light absorption layer, and a transparent conductive film are sequentially formed on a substrate. The backside electrode layer comprises an intermediate layer on the surface that is in contact with the CIS-based light absorption layer, the intermediate layer being composed of a compound of a metal that constitutes the backside electrode layer and a group VI element that constitutes the CIS-based light absorption layer; the intermediate layer comprises a first intermediate layer portion which is formed on the upper surface and a second intermediate layer portion which is formed on the lateral surface that and faces the pattern (P1); and the film thickness of the second intermediate layer portion is larger than the film thickness of the first intermediate layer portion.