PURPOSE: To realize the diagnosis data forming method suitable for the performance of circuit, by forming the input master with the input pattern suited to the input stored in the pattern master in advance, input and output terminal information, common information, and pattern mask coupling.

CONSTITUTION: The pattern suitable for each pattern such as combination of logic, clock, clear reset, and FF input are stored in the pattern master beforehand. A pattern suitable for the circuit is drawn out from the master and the input master is formed with software by adding the pattern to various information such as input and output terminals of circuit, name, number of diagnosis patterns, coupling and selection of circuit and pattern master. Diagnosis data is formed by obtaining correct output with the input master fed to good package thus formed. Further, as shown in diagram, the operation time chart master is formed in advance, and correct output is obtained with good package, allowing to form diagnosis data.