We propose a light therapy device for the treatment of skin barrier function and monitoring of its healing process by transepidermal potential (TEP). The light therapy device incorporates a light guide for irradiating red light and a microneedle salt bridge for TEP measurement. The light therapy device has advantages that it is possible to promote skin barrier recovery by a red light and monitor the recovery process of the skin barrier function by TEP in real time. We measured TEP while irradiating red light for 10 minutes to a skin section in which the barrier function was destroyed experimentally, and observed how TEP returns to the normal TEP. We succeeded in evaluating the barrier recovery effect of red light in real time for the first time by TEP. The light therapy devices will be useful for the treatment of skin inflammation such as atopic dermatitis and the quantitative assessment of its recovery process.