Provided are a photodetector capable of suppressing variations in the output characteristics among photodiodes, and a display device provided with the photodetector. A display device in use has an active matrix substrate (20) including a transparency base substrate (2), a plurality of active elements and a photodetector. The photodetector includes a light-shielding layer (3) provided on the base substrate (2), and a photodiode (1) arranged on an upper layer of the light-shielding layer (3). The light-shielding layer (3) is overlapped with the photodiode (1) in the thickness direction of the base substrate (2). The photodiode (1) includes a silicon layer (11) insulated electrically from the light-shielding layer (3). The silicon layer (11) includes a p-layer (11c), an i-layer (11b) and an n-layer (11a) that are provided adjacent to each other in the planar direction. The p-layer (11c) is formed so that its area (length Lp) will be larger than the area (length Ln) of the n-layer (11a).