A cooling unit including a cooling plate in which a cooling fluid is allowed to flow, the cooling plate has a structure that a pair of plate members are oppositely arranged sandwiching a cooling tube the cooling fluid is to flow, manufactured by a method of manufacturing a cooling unit, the method comprising: A method of manufacturing a cooling unit having a cooling plate in which a cooling fluid is allowed to flow, the cooling plate has a structure that a pair of plate members are oppositely arranged sandwiching a cooling tube the cooling fluid is to flow is disclosed. The method includes: forming a groove for receiving the cooling tube, in at least one opposing surface of the one pair of plate members; and joining each of the one pair of plate members and the cooling tube together by receiving the cooling tube in the groove; wherein, in joining, an external force is applied to at least one of the one pair of plate members whereby deformation is caused in an adjacent point to the groove thereby engaging the adjacent point with the cooling tube.