Provided is a cast-iron cylindrical member having projections (P) formed integrally with a casted surface (an outer peripheral surface), and a composite structure including the cast-iron cylindrical member and an outer periphery-side member. The cast-iron cylindrical member satisfies: (A) 0.50 mm>a height (H) of the projections (P)≥0.20 mm; (B) 180≥a total number (N) of the projections (P) per cm2 of the outer peripheral surface≥61; (C) the projections (P) include a projection (Pn) having a constricted shape; (D) a ratio (NP) of the projections (Pn) to the projections (P)≥50%; (E) a bonding strength index (S) expressed by: S=H2×N×NP is equal to or larger than 310; and (F1) a bonding strength F(Al) obtained when the outer peripheral surface of the cast-iron cylindrical member is cast-in inserted with an aluminum alloy exceeds a boundary bonding strength (Fb) expressed by: Fb=1.325×H2×N−0.75.