An active matrix substrate in which variations in output characteristics of photodiodes are reduced, and a display device using this active matrix substrate, are provided. An active matrix substrate (1) having an n-TFT (20), a p-TFT (30), and a photodiode (10) is used. The photodiode (10) includes a p-layer (7), an i-layer (8), and an n-layer (9). The i-layer (8) includes a p-type semiconductor region (8a) at a position adjacent to the player (7), said p-type semiconductor region (8a) having a diffusion concentration of p-type impurities that is set at the same level as that of a diffusion concentration of p-type impurities in the channel region (23) of the n-TFT (20); and an n-type semiconductor region (8b) at a position adjacent to the n-layer (9), said n-type semiconductor region (8b) having a diffusion concentration of n-type impurities that is set at the same level as that of a diffusion concentration of n-type impurities in the channel region (33) of the p-TFT (30).