To obtain a heat pipe which effectively utilizes a space faced with a heat receiving part, and is high in cooling efficiency, in the self-excited vibration type heat pipe.

A heat pump 2 comprises a flat-plate shaped box 3 having a flow passage 4 sealed with a working fluid. A region Ar for attaching a heat generation source HS is defined at a heat receiving part Hv of one face of the box 3. At the other face side of the box 3, fins 5 are attached to a heat radiation part Hr, and the fins 5 are extended up to the space which the heat receiving part Hv faces. Heat conductivity between the box 3 at the heat receiving part Hv and the fins 5 is lower than a heat conductivity between the box 3 at the heat radiation part Hr and the fins 5. Therefore, calories directly moving to the fins 5 from the heat receiving part Hv can be reduced.