Aiming at proposing a new model which can explain and simulate the
change of office work productivity caused by the change of office environment and/or
workers¡Ç internal factors, the author has discussed the model details by examining the
conventional models and experimental data. The proposed model is based on a tri-state
transition model which consists of a working state, a short-term pause and a long-term
pause. The transition between the working state and the short-term pause is simulated
by a logarithmic normal distribution, while that between the working state and the longterm
pause is caused by probabilistic functions calculated from a mental fatigue (MF) as
a virtual parameter. It is expected that the model framework can not only explain the
office work as a series of human cognitive processes but also predict the change of the
productivity by computer simulation.