With the invention of electric bulbs, human has been living under various illuminant environments. Since the alternative current (AC) power is used for supplier of electric bulbs, intensity difference between consecutive video frames can be captured with high-speed camera. While most of conventional methods focus on only spatial information of a single image, we propose a deep spatio-temporal color constancy method. To exploit the temporal feature from high-speed video, maximum gradient map is fed into the proposed network. It can easily identify image regions which are significantly illuminated by light bulbs and be a useful information for estimating the illuminant. The experimental results demonstrate that using temporal features leads to better performance of illuminant estimation rather than conventional spatial methods.