The importance of personalized information services has been increasing. Description of personal preferences needs to be prepared beforehand to realize such services. We propose a system for automatically acquiring personal preferences from TV viewer’s behaviors. Considering “when” a viewer is watching TV is highly related to the viewer’s preferences, we focus on estimating the time interval during which a pre-registered viewer is watching TV. In this paper, we firstly describe the outline of the personal preference acquisition system, and address a method for estimating the TV viewing intervals based on the appearance of frontal faces. Experiments resulted in a precision rate of 97.1% and a recall rate of 70.6% on average for TV viewing interval estimation.