Spatial Quadrature Amplitude Modulation (SQAM) in which the spatial phase of the signal beam in addition to the spatial intensity is modulated is expected as one of the signal modulation methods to increase the storage capacity of the holographic data storage. In this paper, detection of experimentally generated SQAM signal beam which is holographically recorded and reconstructed is investigated with several measuring methods of complex amplitude of light wave. Single shot detection technique for SQAM signal beam, which is inevitable for a practical perspective, is also discussed.