Beam propagation behavior of the ITER EC equatorial launcher mock-up was investigated at low power level. A 170 GHz, HE11 mode generator was used as a beam source. Maximum intensity at the mirror-edge was −35 dB which was almost background level and no signal was obtained on the beamduct wall. Assuming a radiation from the waveguide nearest to the wall an intensity profile on the beam-duct wall was estimated, the maximum intensity on the beam-duct wall and at the mirror-edge were a level of −40 dB, and of −13dB, respectively. At outlet of the EL mock-up, single peak radiation profile was confirmed and the beam center was located as designed. The peak intensity of the side lobes were about −20 dB which is reasonably small