The physiological mechanism of coupling between neuronal activity, metabolism and cerebral blood flow (CBF) is not clarified enough. In this study, the authors have examined activity-dependent changes in oxygen partial pressure (pO2) and CBF response in an arteriole by 2-dimensional numerical simulation with a mathematical model of O2 transport from the arteriole to its surrounding tissue including an adjusting function of CBF. In the steady state of O2 consumption, an area in the tissue where O2 is supplied from the arteriole becomes smaller as O2 consumption rate of the tissue increases, which is accompanied by increase of CBF. Therefore decrease of the O2- supplied area gradually becomes stagnant. Unsteady responses of the local pO2 and CBF were also examined. The response of pO2 in the upstream area of the arteriole is monophasic increment corresponding to CBF response, whereas the response in the middle area is biphasic response showing an initial decrease followed by a positive peak. In the downstream area, advective flow holds decrement of the pO2. Delay in CBF response to neuronal activity has also been found.