Experiments on a pulsed microwave‐beaming thruster were conducted using a millimeter‐wave, high‐power gyrotrons developed by the Japan Atomic Energy Research Institute. Plasma inside of 2‐dimensional and axsymmetric parabola reflectors were observed using a high‐speed camera. Propagation velocity of the discharge front was well agreed with theoretical prediction assuming nonequilibrium photo ionization. Plasma was found to develop in three directions in a reflector absorbing direct or reflected microwaves. Shock wave propagation velocity varied depending on the distance from focal point and on angle from optical axis. © 2004 American Institute of Physics