To keep the operating environment of the card type electronic device by containing a printed circuit board mounted with heat generating circuit components during operation into the inside of a flat box type casing so as to enhance heat dissipation performance of the circuit components.

Plural 1st vent holes 45 to take external air are made for a rear wall 31e of a casing. Plural 2nd vent holes 47 are made for an upper wall 31b and side walls. In the operating state of a card type electronic device (PC card) 30, circuit components 38 contained in the casing 31 generate heat. In this case, since the casing 31 of the PC card 30 has the 1st vent holes 45 open to the outside of the casing through a card insert port and the 2nd vent holes 47 open to the contained chamber, the heat from the circuit components 38 is emitted to the outside of the casing 31 via the 1st and 2nd vent holes 45, 47. Since the 2nd vent holes 47 are placed adjacent to the circuit components 38, the heat is delivered to the container chamber of the casing through the 2nd vent holes 47 without being diffused in the inside of the casing 31.