Measurements of starting load in the indraft supersonic wind tunnel of Muroran Institute of Technology were conducted for Mach 2, 3 and 4 conditions with AGARD-B model. The high speed photographs were taken for the behaviors of the wind tunnel model. Those photographs make clear that the oscillations of the model coincide with the measured starting load oscillation and starting loads were caused by two shock waves. The first shock wave is the reflection shock, which is generated at the nozzle throat by expansion wave reflection. The second one is asymmetric oblique shock waves (AOS) coming from the upstream. AOS can generate the asymmetric conical shock (ACS) around the nose cone of the model, which would have directly caused the starting loads on the wind tunnel model. Based on those observations, the authors presented the conical shock theory, which is the alternative starting load prediction theory to the normal shock theory.