A detection apparatus to be used with a manipulator, the apparatus comprising a single monocular imaging unit and a single light beam irradiation unit, the detection apparatus is to be provided at the end of the manipulator, and the detection apparatus comprising a computing device, wherein: an optical axis of the imaging unit forms an intersecting angle with a projection of the light beam on a horizontal imaging plane and with a projection of the light beam on a vertical imaging plane, which planes pass through the optical axis of the imaging unit, the horizontal imaging plane being defined as a plane including both of the optical axis of the imaging unit and a horizontal x axis defined in an imaging plane of the imaging unit, and the vertical imaging plane being defined as a plane including both of the optical axis and a vertical y axis defined in the imaging plane of the imaging unit; the computing device is configured to compute a distance L between the light beam irradiation unit and a photographed plane which is orthogonal to a light beam irradiation direction, by obtaining a position of a light beam irradiation point on the imaging plane of the imaging unit and of a light beam irradiation point on the photographed plane; in the computing, the distance L corresponding to the obtained position of the light beam irradiation point on the imaging plane is obtained using a relational expression previously formed based on: 1) a position (xi, yi) (i=0, 1,.. N) of the light beam irradiation points on the imaging plane; and 2) an actually measured value Li of distances L between the photographed plane and the light beam irradiation unit for a respective position (xi, yi) of the light beam irradiation points on the imaging plane; and a relative distance between the light beam irradiation point and a hand coordinate point, which is a coordinate of a joint point to which the detection apparatus is to be mounted and is computed based on kinematics of the manipulator, and is obtained based on the obtained corresponding distance L. an optical axis of the imaging unit forms an intersecting angle with a projection of the light beam on a horizontal imaging plane and with a projection of the light beam on a vertical imaging plane, which planes pass through the optical axis of the imaging unit, the horizontal imaging plane being defined as a plane including both of the optical axis of the imaging unit and a horizontal x axis defined in an imaging plane of the imaging unit, and the vertical imaging plane being defined as a plane including both of the optical axis and a vertical y axis defined in the imaging plane of the imaging unit; the computing device is configured to compute a distance L between the light beam irradiation unit and a photographed plane which is orthogonal to a light beam irradiation direction, by obtaining a position of a light beam irradiation point on the imaging plane of the imaging unit and of a light beam irradiation point on the photographed plane; in the computing, the distance L corresponding to the obtained position of the light beam irradiation point on the imaging plane is obtained using a relational expression previously formed based on: 1) a position (xi, yi) (i=0, 1,.. N) of the light beam irradiation points on the imaging plane; and 2) an actually measured value Li of distances L between the photographed plane and the light beam irradiation unit for a respective position (xi, yi) of the light beam irradiation points on the imaging plane; and a relative distance between the light beam irradiation point and a hand coordinate point, which is a coordinate of a joint point to which the detection apparatus is to be mounted and is computed based on kinematics of the manipulator, and is obtained based on the obtained corresponding distance L. in the computing, the distance L corresponding to the obtained position of the light beam irradiation point on the imaging plane is obtained using a relational expression previously formed based on: 1) a position (xi, yi) (i=0, 1,.. N) of the light beam irradiation points on the imaging plane; and 2) an actually measured value Li of distances L between the photographed plane and the light beam irradiation unit for a respective position (xi, yi) of the light beam irradiation points on the imaging plane; and 1) a position (xi, yi) (i=0, 1,.. N) of the light beam irradiation points on the imaging plane; and 2) an actually measured value Li of distances L between the photographed plane and the light beam irradiation unit for a respective position (xi, yi) of the light beam irradiation points on the imaging plane; and a relative distance between the light beam irradiation point and a hand coordinate point, which is a coordinate of a joint point to which the detection apparatus is to be mounted and is computed based on kinematics of the manipulator, and is obtained based on the obtained corresponding distance L.