This research aims to clarify the characteristics of human behavior while eating meals in co-eating and solitary eating situations. To manipulate eating situations, we observed participants' behaviors ( N = 6) under two different experimental settings: a solitary eating condition, in which participants had their meals alone while watching television or using their cellphone, and a co-eating condition, in which participants ate their meals in the course of dyadic conversation with friends. We assessed the participants’ gaze behaviors and eating actions during the meal and compared these between the two eating situations statistically. The results demonstrate that 1) participants in the co-eating condition glanced longer at their own meal compared to participants in the solitary eating condition, 2) participants in the solitary eating condition often stopped their other eating actions while chewing food, and 3) participants in the co-eating condition frequently gathered meal portions using a spoon while looking at their meal. These results suggest that participants in the solitary eating condition enjoyed their meal while watching television or using their cellphone in an informal atmosphere. Meanwhile, participants in the co-eating condition used their meals to coordinate their interactive behaviors with a co-eater. The social functions of co-eating are discussed from a human behavior analysis perspective.