According to an instruction manual generated by an instruction manual generator, a process log of a practical process performed by a plurality of instruction executers is acquired. A command described in the instruction manual is extracted, and extracted commands are extracted from each process log. The sections of the process logs sectioned by the extracted commands are numbered, and the number of executions of the commands different from the extracted command is counted. When the variance of the number of the executions of a command in a section common in the plurality of process logs is larger than a specified value, the possibility of an unclear description in the corresponding section in the instruction manual is displayed for notification of a different process performed for each instruction executer.