An ECU stores and holds in a memory unit NOx information which is information concerning NOx in an exhaust gas flowing through an exhaust system of an onboard engine of a vehicle or NOx purification by a catalyst placed in the exhaust system. The ECU includes a parameter acquisition unit that acquires an NOx parameter, which is an outflow quantity of NOx flowing out to a downstream side of the catalyst or a correlation value correlating to the outflow quantity of NOx, according to a working state of the engine, an integrated value computation unit that computes a parameter integrated value by integrating NOx parameters acquired by the parameter acquisition unit, and a storage processing unit that stores in the memory unit the parameter integrated value as the NOx information.