An intake controller installed in a diesel engine, wherein the control part of a valve controller fully opens a bypass valve in a bypass passage when it determines that the operating state of the diesel engine is suddenly decelerated from a middle and high speed and middle and high load range. Accordingly, the control part can feed an intake air from the outlet passage side of a compressor to the inlet passage side of an exhaust turbine, and can rapidly lower the rotational speed of an exhaust turbine supercharger (20) which tends to be rotated at a high speed by inertia. As a result, since the operating state not enter a surging area while an operating point is moving, surging can be securely avoided.