1. A medical guiding system comprising: a detection portion for detecting at least one of a position and an orientation of a medical instrument and at least one of positions and orientations of a plurality of feature points of a subject; a storage portion for storing reference image data having anatomical positional information on at least one of a viscus and an organ of a human body; and a guide image creation portion for creating a guide image indicating a position of the medical instrument or an observation position by the medical instrument with respect to the subject based on the reference image data, wherein the guide image creation portion calculates the position of the medical instrument or the observation position by the medical instrument with respect to the subject, based on at least one of the position and the orientation of the medical instrument and at least one of the positions and the orientations of the feature points of the subject which are detected by the detection portion, and creates a guide image by correcting the calculated position of the medical instrument or the calculated observation position by the medical instrument, using the positions of the plurality of feature points.