We have successfully developed a novel micromechanism of random number generator (RNG) by using the silicon micromachining technique. The MEM(Micro Electro Mechanical)RNG produce a series of random numbers by using the pull-in instability of electrostatic actuation operated with a typical dc 150 volt. The MEM RNG is made by the deep reactive ion etching of a silicon-on-insulator(SOI) wafer, and is very small compared with the conventional RNG hardware based on the randomness of thermal noise or isotope radiation. Quality of randomness has been experimentally confirmed by the self-correlation study of the generated series of numbers. The MEM RNG proposed here would be a true random number generation, which is needed for the highly secured encryption system of today’s information technology.