A substrate mounted with an electronic element thereon, comprises a base, an insulator, a fluid passage, and a pressurizer. The base is made of a metal. The insulator is made of a ceramic material and provided on one face of the base. The insulator has a heat-generating electronic element mounted on its side facing contrary to the one face. The fluid passage is formed within the base to have liquid flow therethrough, and radiates heat which has been transmitted from the electronic element via the insulator to the base. The pressurizer applies pressure to the liquid within the fluid passage. The pressurizer includes a pressurizing chamber and an actuator unit. The pressurizing chamber is formed within the fluid passage. The actuator unit changes a volume of the pressurizing chamber by displacing a portion of the insulator corresponding to the pressurizing chamber with respect to a direction perpendicular to the one face.