A laser annealing apparatus according to an embodiment includes a laser light source, an annealing optical system, a linear irradiation region along a Y-direction, a moving mechanism configured to change a relative position of the irradiation region with respect to the substrate along an X-direction, an illumination light source configured to generate illumination light for illuminating the substrate along a third direction, and a detector configured to detect detection light reflected, in a fourth direction, on the substrate illuminated by the illumination light so as to photograph an annealed part of the substrate in a linear field of view along the Y-direction. In a YZ-plane view, the third direction is inclined from the vertical direction and the fourth direction is inclined from the vertical direction.