An optimization device includes: a plurality of search parts; and a controller that controls the plurality of search parts, wherein, each of the plurality of search parts includes a state holding part configured to hold each of values of a plurality of state variables included in an evaluation function representing an energy value, an energy calculation part configured to calculate a change value of the energy value generated in a case where any one of the values of the plurality of state variables is changed, and a transition controller configured to stochastically determine whether or not to accept a state transition by a relative relation between the change value of the energy value and thermal excitation energy, based on a set temperature value, the change value, and a random number value.