A microorganism detecting device comprising: a sampling section adapted for taking a sample from a detection target, a sample concentrating section adapted for concentrating the microorganisms existing in the sample taken in the sampling section, said sample concentrating section including filtering means for collecting the microorganisms, a reagent adding section adapted for adding a reagent having a component which changes the reagent color tone by existence of the microorganisms to the sample concentrated in the sample concentrating section, a microorganisms detecting section adapted for detecting the change of the color tone of the reagent added to the sample in the reagent adding section by means of an optical system, a detected result outputting section adapted for outputting the detected result detected in the microorganisms detecting section, and a controller adapted for controlling the sampling section, the sample concentrating section, the reagent adding section, the microorganisms detecting section, and the detected result outputting section, characterized in that the sample concentrating section and reagent adding section comprise a microorganism detecting test tube, the filtering means being provided at the bottom of the microorganism detecting test tube, and a drain tank under the microorganism test tube being connected to a discharging valve and a vacuum pump, wherein the sample concentrating section further includes culturing means by supplying a culture medium to the filtering means via the microorganism detecting test tube, and wherein the reagent adding section supplies the reagent to the filtering means via the microorganism detecting test tube. a sampling section adapted for taking a sample from a detection target, a sample concentrating section adapted for concentrating the microorganisms existing in the sample taken in the sampling section, said sample concentrating section including filtering means for collecting the microorganisms, a reagent adding section adapted for adding a reagent having a component which changes the reagent color tone by existence of the microorganisms to the sample concentrated in the sample concentrating section, a microorganisms detecting section adapted for detecting the change of the color tone of the reagent added to the sample in the reagent adding section by means of an optical system, a detected result outputting section adapted for outputting the detected result detected in the microorganisms detecting section, and a controller adapted for controlling the sampling section, the sample concentrating section, the reagent adding section, the microorganisms detecting section, and the detected result outputting section, characterized in that the sample concentrating section and reagent adding section comprise a microorganism detecting test tube, the filtering means being provided at the bottom of the microorganism detecting test tube, and a drain tank under the microorganism test tube being connected to a discharging valve and a vacuum pump, wherein the sample concentrating section further includes culturing means by supplying a culture medium to the filtering means via the microorganism detecting test tube, and wherein the reagent adding section supplies the reagent to the filtering means via the microorganism detecting test tube.