A variable throat device for an air compressor, which is disposed in an air suction passage of an air compressor, and may secure reliable flow control by changing a cross-sectional area of the passage through application of force to the passage, significantly reduce a possibility of unsteady flow by suppressing generation of a vortex in an air stream, secure a desired flow rate without pressure loss in the air stream, and reduce fatigue load applied to a compressor impeller through stabilization of suction flow in order to achieve significant reduction of vibration of the impeller is provided.