I. Introduction
Objective emotion estimation in daily life is useful and required for psychological research, marketing, and evaluating user experience. The internal states of humans, such as emotions, appear as changes in various physiological signals such as electrocardiogram (ECG), electrodermal activity (EDA), electroencephalography (EEG), and facial expressions [1]–[3]. It has been reported that emotions can be estimated more accurately by analyzing a combination of multiple physiological signals [4], [5]. Many studies have evaluated product prototypes and media contents in practical environments by measuring and analyzing multiple physiological signals [6]–[8].