PROBLEM TO BE SOLVED: To provide technology for securing a coolant flow rate suitable for required cooling performance.SOLUTION: In a semiconductor lamination unit, a center axis J1 of a supply tube 7 is decentered further away from the center of a cooling plate 2a in the longitudinal direction thereof than a center axis J3 of a connection tube 5, and an inside fringe 7a of the supply tube 7 is positioned further away from the center of the cooling plate 2a in the longitudinal direction thereof than an inside fringe 5a of the connection tube 5. Coolant is made to flow more in a further remote place than the inside fringe 5a of the connection tube 5 right after it enters from the supply tube 7, and a coolant flow rate entering a lateral passage 15a of the cooling plate 2a is thereby decreased by decreasing the coolant hitting the inside fringe 5a. Also, a coolant flow rate flowing toward downstream cooling plates 2b-2j through a vertical passage 15b of the connection tube 5 is increased. Thereby, compared with the cooling plate 2a in which an abutting region of a semiconductor package 3 is present only on one side, the coolant flows more to the cooling plates 2b-2j in which the abutting region of the semiconductor package 3 is present on both sides.