The beam measuring apparatus of the present invention includes a detection device including a shield member that has an edge, and a detector configured to detect the beam of which at least a part is not shielded by the shield member; a relative movement mechanism configured to cause a relative movement between the shield member and the beam; and a controller configured to control the detection device and the relative movement mechanism so as to cause one of the edge and the beam to traverse the other with respect to each of a plurality of points on the edge, to sum a plurality of signals, respectively obtained by the detection device with respect to the plurality of points and with respect to relative positions of the relative movement corresponding to one another, so as to obtain a signal sequence, and to obtain the characteristic based on the signal sequence.