Population aging is increasingly serious. The application of social robots for home-based elder care is an important way to solve this problem. Aging adults' demands for social robots' companionship affect robotic designs. This study aimed to investigate aging adults' demands for social robots' companionship and explored in which life situations it was appropriate to accompany aging adults by social robots. This study involved three phases. Phase 1 (an interview survey) collected the life situations in which aging adults lived alone at home. Based on the results of Phase 1, Phase 2 (a questionnaire survey) investigated aging adults' demands for companionship, whereas Phase 3 (an expert evaluation) investigated the feasibility of the robots' companionship for aging adults. After the three phases, this study compared aging adults' demands for companionship with the feasibility of social robots' companionship in each life situation. Based on the results, the life situations of dinning and watching TV, there was a greater likelihood that the companionship that aging adults needed might be provided by social robots. In the life situations of sleeping and short breaking, it was difficult that aging adults' demands for companionship were fulfilled by social robots. Implications were discussed for home-based elder care system.