Effect of far-red light on lesion development in broad bean leaflets inoculated with Alternaria tenuissima was investigated. Lesion development by A. tenuissima was significantly inhibited under red light. Furthermore, red light-induced resistance was observed even in additional far-red light treatment. In the far-red light conditions, however, large lesions were induced and the lesion size was similar to that in broad bean leaflets in the dark. Our study showed that red light is required for the suppression of lesion developed in broad bean against A. tenuissima, whereas far-red light had no suppressive effect to the resistance of broad bean.