A warning device checks for errors in design object data and issues a warning for detected errors by storing allowance information, which allows issuance of warning prevention, cancel information, which cancels relevant allowance information to permit issuance of warning for each error identification, and instruction identification, which identifies an edit command for editing generated design object data for error identification. When said edit command is accepted, the error identification for the instruction identification of edit command is acquired. Cancel information can be registered for error identification. Respective errors corresponding to error identifications are checked, when an operation for checking the design object data is accepted, and when a type of an error is identified, whether to issue a warning based on the allowance information and cancel information for relevant error identification is determined.