Aiming to reveal the mechanism of intellectual productivity variation of office workers, the authors analyzed the behavior of subjective experiment assuming office work, and proposed an intellectual productivity model. The model is a three state transit model assuming "working state", "short-term rest state" and "long-term rest state". A subject experiment was conducted where illuminance on the desk and work motivation were controlled to vary their productivity. The result was analyzed with this model and it is confirmed that the model can explain the productivity variation. © 2013 Springer-Verlag Berlin Heidelberg.