There is described an apparatus for making metal oxide particles which are substantially free of coarse tail from an oxidizing agent and a metal reactant in a flow reactor. Furthermore, a method for cleaning a workpiece and a cleaning device are suggested. It is also possible for the alternately generated low frequency to be lower than the basic frequency in a range from 5 to 200 Hz, and for the interval during which the basic frequency is supplied to be gradually increased and decreased at specified times. Mixing the outgoing lights of the light source passing through light-valving structure, the color-adjusting structure, and the overlapping structure to obtain a different wavelength band from that of the light source.