Abstract: An ejector including a nozzle communicating with a fluid inlet, a diffuser communicating with a fluid outlet, and a decompression chamber placed between the nozzle and he diffuser. The ejector is arranged to generate a negative pressure in the decompression chamber by a fluid ejected from the nozzle. A target negative pressure P in the decompression chamber is set in a range of “40 kPa<P?50 kPa”. A SD/Sd ratio between a sectional area SD of an inlet of the diffuser and a sectional area Sd of an outlet of the nozzle is determined to meet a relation: “1.20?SD/Sd?4.08?0.047P”.

Abstract: A negative pressure supply apparatus for brake booster, arranged to supply an intake-pipe negative pressure in an engine intake system to a brake booster mounted in a vehicle, comprises a negative pressure supply part communicated with a bypass passage which allows part of air flowing in the intake pipe to bypass the intake pipe and supplies the intake-pipe negative pressure to the brake booster; an air ejector part placed in the bypass passage to increase the intake-pipe negative pressure and supply the increased negative pressure to the brake booster; and an open/close device including a temperature-sensitive medium, the device being placed in the bypass passage upstream of the air ejector part and configured to open and close the bypass passage.