A detection device includes an illumination optical system configured to illuminate a first alignment mark for detecting a position of an object in a first direction and a second alignment mark for detecting a position of the object in a second direction and a detection optical system configured to detect light beams from the alignment marks. The illumination optical system includes an optical element disposed at a position optically conjugate to a surface to be illuminated, and the optical element includes a region configured to form an illumination light beam for illuminating a first portion of the surface to be illuminated with a first angular distribution and a region configured to form an illumination light beam for illuminating a second portion of the surface to be illuminated with a second angular distribution.