A random number generator generates a random number by using at least two algorithms. A security device includes the random number generator. The random number generator includes a random seed generator and a post processor. The random seed generator is configured to receive an entropy signal and to generate a random seed of a digital region generated by using the entropy signal. The post processor is configured to generate a random number from the random seed by using a first algorithm and a second algorithm. A bias property represents unbiasedness of a result value, and a bias property of the first algorithm is different from a bias property of the second algorithm.