A symbolic execution device, a symbolic execution method, and a probability distribution update method for symbolic execution are provided. The symbolic execution device includes a storage unit for storing at least one of a first probability distribution and a second probability distribution and a processor for sampling and obtaining a weight vector from the first probability distribution, for sampling and obtaining a removal rate from the second probability distribution, for adding the weight vector to at least one feature vector obtained from at least one candidate state to obtain a score for each of the at least one candidate state, and for selecting a state to be removed from among the at least one candidate state by using the score of each of the at least one candidate state and the removal rate.