To provide a metal member uniting structure in which a pair of metal members can be stably fastened to each other with appropriate fastening axial force and in which it is possible to surely prevent generation of clearance and deformation caused by excessive axial force in the vicinity of the position where the axial force affects when the temperature increases or decreases.

A cylinder head (a first metal member) whose coefficient of linear expansion is the first coefficient A and a cylinder block (a second metal member) whose coefficient of linear expansion is the second coefficient B different from the first coefficient are united to each other by a bolt (a third metal member). The coefficient C of linear expansion of the third metal member is the third coefficient C between the first coefficient A and the second coefficient B. When a first distance between a first united portion p1 of the first metal member and the third metal member and a second united portion p2 of the first metal member and the second metal member is denoted by X and a second distance between a third united portion p3 of the second metal member and the third metal member and the second united portion p2 is denoted by Y, the following equation (A-C)X=(C-B)Y is fulfilled.