A control device of a nitrogen oxide sensor comprises a voltage control part configured to control voltage applied to the pump cell, and a temperature estimation part configured to estimate a temperature of the pump cell. The voltage control part is configured to make the voltage applied to the pump cell a voltage of a starting voltage of decomposition of water or more when the estimated temperature of the pump cell estimated by the temperature estimation part is within a predetermined temperature region of less than an activation temperature of the pump cell as control suppressing evaporation.