1. An information processor which detects factors, in a video, influencing health, comprising: an image input unit which receives a series of image data to process a plurality of consecutive still images constituting the video; a feature-quantity calculation unit which calculates a feature quantity of each of the still images on the basis of the image data; a conditional-expression storing unit which stores a conditional expression, for each factor, to determine whether each of the still images produces the factor on the basis of the corresponding feature quantity; a factor determination unit which determines, for each factor, whether each of the still images produces the factor on the basis of the corresponding feature quantity and the corresponding conditional expression; and an image-list display unit which displays, for each factor, a list of information indicating the still images determined to produce the factor.