1. A computer-readable medium storing therein a data conversion program that causes a computer to execute a process comprising: receiving after a schema of a database has been changed from a former schema to a new schema, a processing request concerning the database; judging based on difference information concerning the former schema and the new schema, whether in the processing request, a condition that specifies process data subject to processing, has been changed by the new schema; searching the database for conversion data whose format is to be converted from the former schema to the new schema, the searching based on judgment results obtained at the judging and on the processing request; and converting the format of the retrieved conversion data, from the former schema to the new schema.