In this study, aiming at proposing a model which can explain and simulate the change
of productivity, the author has conducted a subject experiment and discussed the details of the model
by comparing the results of the computer simulation based on the model with the experimental results.
Concretely, the model employs a working state, a non-working state and a value BF which is assumed
as a brain fatigue. Office workers are assumed to transit these two states along with the probabilistic
functions based on the variation of BF. From the internal parameters of the model to explain the
probabilistic functions examined by the experimental results, it was found that the subjects tend to
concentrate the task when the remuneration is provided, and they try to keep their attention to the
task and take a long break instead when the task workload is high.