In this study, Mach number effect on edgetone is investigated to verify the feedback-loop of edgetone using the high-order computation. The computational results show three clear points. When the Mach number increases independently, 1) the edgetone phenomenon tends to cease 2) the frequency of edgetone becomes lower 3) the oscillation mode (which is named stage) of edgetone becomes lower. The second point shows that the edgetone mechanism is explained by the fluid-acoustic feedback-loop. As for the Powell's feedback-loop equation our computational results show that phase-lag p is constant Therefore the feedback-loop equation is verified to be physically correct. However the computed value of p is -0.2 which does not correspond to that of Powell's suggestion.