The present invention relates to a diffuser of a centrifugal compressor for guiding a fluid flowing from an impeller (1) to a scroll (4). The diffuser is formed by a pair of oppositely disposed lateral walls (2), (3). The diffuser is provided at a fluid outlet portion (7) thereof with an outlet throttling portion (7a). This outlet throttling portion (7a) is formed by gradually narrowing the passage width downstream from a starting point (10) which is located in a position at which the fluid dynamic pressure is almost perfectly changed to a static pressure. The provision of the outlet throttling portion (7a) decreases the risk of a pressure loss, restrains the possibility of flow separation and prevents the fluid from reversely flowing from the scroll (4). This results in improvements in surge line and partial load efficiency.
