A microwave reflectometer is developed for electron density profile measurement in Heliotron J. An amplitude modulation (AM) type system is adopted to reduce density fluctuation effects. The carrier frequency ranges from 33 to 56 GHz, and the modulation frequency is 200 MHz. The X-mode is selected as the propagation mode in order to measure a hollow density profile which is typically observed in ECH plasmas. A test-bench examination using an aluminum reflection plate shows that the measured phase shift agrees well with that expected from the change in the plate position. The initial measurement results show that the reconstructed density profile has hollow profile at low density and steep gradient at the edge in ECH plasma. The hollowness is weakened as the averaged density increases. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim