To provide a mounting structure of a diode on a printed wiring board having excellent heat radiation properties and advantageous in terms of cost.

In a mounting structure of inserting lead lines 1a, 1a of the diode 1 into through holes 2a, 2a of a printed wiring board 2 so as to be fixed to a wiring pattern by solder 3a, 3a, a heat radiation plate 4 having a recess 4a into which the diode 1 is fitted is set upright on a diode mounting place of the printed wiring board 2 to fit the diode 1 into the recess 4a, and the lead lines 1a, 1a are tightly fixed to the heat radiation plate 4 by solder 3b, 3b. Heat generated in the diode 1 is quickly transmitted to the heat radiation plate 4 through a heat conduction path formed of the lead line 1a and the solder 3b, and efficiently radiated from the surface of the heat radiation plate 4. Accordingly, it is possible to use an inexpensive so-called straight product not excellent in heat radiation properties as the diode, and this is advantageous in terms of cost.