Radioactivity exposure amount of workcraftmen is obtained through simulation by using an operation processor when the workcraftmen carry out work operation within an area under controlled radioactivity. The movement of the workcraftmen carrying out work operation in the area under controlled radioactivity is simulated by making use of layout graphic data relating to the area. The radioactivity exposure amount of the workcraftmen is calculated in response to the simulated movement of the workcraftmen. The operation procedures of the target work operation for radioactivity exposure amount calculation is outputted from the operation processor, when the calculated radioactivity exposure amount satisfies a predetermined value.