Not only facial expressions but also body gestures and postures play an important role in non-verbal communication. Facial expressions are based on two factors: arousal and pleasant emotions, while it is not clear that body gestures and postures have the same structure as the facial expressions have. We indicate that (1) the sitting postures have the same emotion structure as facial expressions and (2) can be measured by pressure sensors on a chair and accelerometers on the body, which predict the emotion factors. We find the sitting postures have three semantic factors: "arousal", "pleasantness", and "dominance", so emotion expressions of the sitting postures are similar to those of the facial expressions. Their difference is "dominance" expressed by not the main body but the body parts such as arms and legs. We conclude that (1) the three factors can be measured with the proposed sensors and (2) the body trunk and the body parts: neck, arms, and legs are important.