Provided is a method of tracking a swimming path of a bacterium which can exactly track the swimming path of the bacterium by modeling the bacterium as ellipsoidal in shape based on an image of the bacterium obtained while the ellipsoidal bacterium swims near a solid surface. The method of tracking a swimming path of a bacterium which is formed in an ellipsoidal shape and swims in a swimming space formed between a solid surface and an imaginary surface parallel to the solid surface includes the steps of: transfecting a fluorescent gene into the bacterium; arranging the bacterium in the swimming space to swim; totally reflecting light irradiated to the solid surface, and forming an evanescent field in the swimming space; taking a picture of the bacterium expressing the fluorescent gene, which emits light in the evanescent field, at respective moments while the bacterium swims, and obtaining an image of the bacterium expressing the fluorescent gene at the respective moments; and fitting the image of the bacterium obtained at the respective moments to an ellipsoidal shape, and setting the shape of the bacterium as the ellipsoidal shape and a position of the bacterium with respect to the solid surface.