The invention discloses an automatic detection instrument for stool specimen, comprising an automatic controller; a dilution device used for adding quantitative diluent into the stool specimen; a stirring and blending device used for stirring and blending the diluted stool specimen; a detecting unit used for detecting the stool specimen, and an aspirating and cleaning device connected with the detecting unit through pipelines and used for transmitting the stool specimen to the detecting unit and cleaning the detecting unit and the connecting pipelines after detection. The detection instrument of the invention can automatically carry out quantitative dilution, physical microscopic examination and partial chemical detection for specimen completely in comparatively sealed pipelines, thereby reducing the link of air contact, reducing the contamination for the environment and laboratory, and improving the work efficiency by using computer software for automatic control.