A stimulated plasma wave experiment by the EXOS-B satellite showed the appearance of echoes of plasma waves with a delay time of several msec. We examined the frequency dependence of the echoes in comparison with the observed plasma resonances and the dispersion relation of plasma waves. The propagation mode of the echoes was identified as the electrostatic electron cyclotron harmonic (ESCH) waves. The appearance regions were examined with respect to the electron density profiles in the magnetosphere that have been determined by measuring the frequencies of stimulated plasma resonances. The ESCH echoes are frequently observed in a detached plasma region. Near the plasmapause the apperance of echoes is significantly frequent in regions where the plasma density is rapildy increasing in the plasmasphere due to a strong supply from the ionsphere. Because of their propagation mode and the state of the plasma density profiles in their appearance regions in the magnetosphere, the echoes are inferred to be produced by the reflection of propagating ESCH waves from small-scale density irregularities of environmental plasma. ¿ American Geophysical Union 1988