A random number generator, a random number generating circuit, and a random number generating method are provided. The random number generating circuit includes the random number generator and executes the random number generating method. The random number generator includes a shift register having N storage elements and a combinational logic circuit. The N storage elements receive a random seed in a static state and repetitively perform a bit shift operation in a plurality of clock cycles. The combinational logic circuit generates an output sequence based on the random seed and a random bitstream received from an external source.