An automatic physiological assay device analyzes light reflected by an assay device and prevents ambient light from interfering with the assay device. The automatic physiological assay device in accordance with the present invention comprises a chassis, an assay device connector assembly, an assay device and a light detecting device. The chassis comprises closed bottom, multiple sidewalls, an inner cavity, an open top and a removable top cover. The assay device connector assembly is mounted slidably through a sidewall and comprises an outer end, two sides and a cover. The cover is mounted on the outer end, seals the sidewall and keeps ambient light away from the assay device. The light detecting device is mounted in the inner cavity and on top edges of guides adjacent the assay device connector assembly.