There is growing awareness of global environmental conservation and the regulations on fuel consumption and exhaust emissions of automobile engines have been strengthened. In recent years, especially, due to the spread of fuel efficiency improving technologies such as downsizing, miller cycle and super lean burn, a wider operating range centrifugal compressor for turbochargers which achieves a high-pressure ratio in a wide operating range has been in high demand. On the other hand, since a compressor is operated under pressure pulsation caused by air intake of an engine, its internal flow exhibits a complicated unsteadiness, which has made it difficult to grasp the flow phenomena toward enhancement of the operating range. Therefore, we conducted a flow measurement using a pulsation test device which replicates an actual engine, and by applying an unsteady numerical analysis with the test result as the boundary condition, we conducted the analysis of the detailed flow structure in the pulsating flow which had not been revealed so far. The result showed that in the pulsating flow, the Helmholtz resonance frequency of a pipe had a large effect on the operating range and the change of the flow pattern due to the appearance or disappearance of full stall at the impeller tip was predominant.