A composite structural body (A) includes a first metal member (M1) having a plate-like shape, a second metal member (M2) having a plate-like shape, and a resin member (R) that integrates the first metal member (M1) and the second metal member (M2) with each other. The resin member (R) includes a first resin layer (R1) that coats astride one main surface of the first metal member (M1) and one main surface of the second metal member (M2), and a second resin layer (R2) that coats astride another main surface of the first metal member (M1) and another main surface of the second metal member (M2). The composite structural body (A) is provided as a composite structural body that has satisfactory moldability, that is capable of securing sufficient strength, and that is suitable as a component of a structure such as a vehicle body.