PURPOSE: To permit the desirable brake power control by forming a casing surrounding a blower and a transmission system for transmitting the engine power to the blower and forming an intake passage for supplying intake through the circulation on the periphery of the transmission system and an intake passage which is closed to stop the feed in an engine high speed range.

CONSTITUTION: In an engine low speed range, an intake passage 9 for the flow of intake B from the periphery of a transmission system 3 and also an opening/ closing valve 3 are opened, and intake A is introduced also from an intake passage 8 of a sleeve 12 side, and a large quantity of intake is supplied into a blower 1 and the corresponding brake power is generated. Further, in an engine low speed range, the opening/closing valve 13 is closed, and the inflow of the intake A supplied from the intake passage 8 is cut off, and the intake B is introduced into the blower 1 only from the intake passage 9 on the periphery of the transmission system 3. Therefore, the intake throttle effect for the blower 1 can be applied, and the generation of the abrupt shock by the brake application by the blower 1 in the engine high speed range can be prevented. Further, the cooling for the transmission system 3 can be secured by the flow of the intake B on the periphery of the transmission system 3.