A received light signal of the measurement light which is reflected from the subject and is then incident on a distance image sensor is acquired from the distance image sensor and a distance image is generated on the basis of the acquired received light signal. The position of a leading end of a medical instrument inserted into the subject is acquired. A leading end position image indicating the position of the leading end of the medical instrument in the subject is acquired. A projection image which is projected to the subject and corresponds to a surface shape of a corresponding part of the subject corresponding to the position of the leading end is generated from the leading end position image, on the basis of the shape of the subject detected from the distance image and the position of the leading end. The projection image is projected to the corresponding part.
