A laser beam irradiation detection device (10A, 10B, or 10C) comprising: a bandpass filter (3a, 3b, or 3c) configured to allow a light ray of a predetermined band including a wavelength band of a color of a laser beam, which is a target of detection, among light rays from a subject to pass therethrough; an imaging unit configured to image the light ray passing through the bandpass filter (3a, 3b, or 3c); and characterised by a histogram generator configured to generate a histogram by analyzing a frequency for each brightness level of a video signal generated based on an imaging signal output from the imaging unit to detect a peak at which the frequency protrudes at a specific brightness level; a light ray trajectory detector configured to detect a trajectory of a light ray in a frame of the video signal, and to detect that the trajectory of the light ray is a trajectory of a straight light ray, when any three bright spots Pa, Pb, and Pc on the trajectory of the light ray satisfy ax+by+c=0 with a, b, and c as constants and x and y as variables; a determiner configured to determine that the trajectory is the trajectory of a light ray formed by the irradiation by a laser beam, when the peak detected by the histogram generator exists at the specific brightness level of the histogram, and a trajectory of a straight light ray exists in the frame; and an emission position detector configured to detect that a first end portion of the trajectory of the straight light ray is a laser beam emission position, when the first end portion exists in the frame, a brightness level decreases from the first end portion side to a second end portion side, the second end portion being located in the frame or at an end portion of the frame, and a condition that a bright spot on the second end portion side moves in an arc shape is satisfied. a bandpass filter (3a, 3b, or 3c) configured to allow a light ray of a predetermined band including a wavelength band of a color of a laser beam, which is a target of detection, among light rays from a subject to pass therethrough; an imaging unit configured to image the light ray passing through the bandpass filter (3a, 3b, or 3c); and characterised by a histogram generator configured to generate a histogram by analyzing a frequency for each brightness level of a video signal generated based on an imaging signal output from the imaging unit to detect a peak at which the frequency protrudes at a specific brightness level; a light ray trajectory detector configured to detect a trajectory of a light ray in a frame of the video signal, and to detect that the trajectory of the light ray is a trajectory of a straight light ray, when any three bright spots Pa, Pb, and Pc on the trajectory of the light ray satisfy ax+by+c=0 with a, b, and c as constants and x and y as variables; a determiner configured to determine that the trajectory is the trajectory of a light ray formed by the irradiation by a laser beam, when the peak detected by the histogram generator exists at the specific brightness level of the histogram, and a trajectory of a straight light ray exists in the frame; and an emission position detector configured to detect that a first end portion of the trajectory of the straight light ray is a laser beam emission position, when the first end portion exists in the frame, a brightness level decreases from the first end portion side to a second end portion side, the second end portion being located in the frame or at an end portion of the frame, and a condition that a bright spot on the second end portion side moves in an arc shape is satisfied. <EOS>