In this paper, we describe an investigation into users' experiences of a simple talking robot with back-channel feedbacks that is designed based on an artificial subtle expression (ASE). In the experiments with participants, they are divided into six conditions based on an expression factor (three levels; human-like speech, blinking light, and beeping sound) and a timing decision method factor (two levels; a linguistic method and an acoustic method) for investigating participants' impressions on the dialogue experience. We developed an electric pedestal to show the blinking expression, on which a simple cubic robot was fixed. Participants engaged in a task of explaining a cooking procedure with a spoken dialogue system coupled with the robot on the pedestal. The robots responded to them by making the back-channel feedbacks in accordance with the expression factor. The results of questionnaire analyses suggested that the ASE-based expressions of back-channel feedback provide positive experiences for users.