We are presenting the results of outdoor experiments fora vertical single-effect diffusion solar still. This structure is equivalent to the first distilling cell of a vertical multiple-effect diffusion solar still, coupled with a flat plate reflector. The proposed multiple-effect still has a very high rate of productivity in spite of its simple structure and it may be possible for local technicians in the developing countries to construct and maintain the still. First, we performed theoretical analysis to determine the optimum angle of the flat plate reflector and the optimum orientation of the still, both of which would vary according to month, throughout the year at Kurume, Japan (33.2 degrees N latitude) assuming that the angle of the flat plate reflector is fixed throughout the day and the orientation of the still is changed just once a day at southing of the sun. After that, we performed outdoor experiments with the vertical single-effect diffusion still coupled with the flat plate reflector from July to November 2005 at Kurume, Japan. Time variations of the distillate production rate of the still as well as temperatures in the still showed a fairly good agreement between the experimental results and the theoretical predictions, and the experimental results of the daily productivity of the still agree with the theoretical predictions with about a 7% error margin except for the results on a cloudy day. This indicates that the solar absorption of direct, diffuse and reflected radiation on the first partition of the proposed still can be well calculated with a geometrical model described in our previous paper [23].