A state monitoring device (100) is mounted in a vehicle (1) and monitors the state of a driver using a face image (50) of the driver. The state monitoring device emits light toward a defined area (PA) from a light emitting unit (15), and receives light reflected by the face of the driver by an image pickup unit (10), the face of the driver being assumed to be located in the defined area. A control circuit (20) of the state monitoring device adjusts the gradation level of the face image by changing the length of an exposure period in which an image pickup element (11) of the image pickup unit is maintained in an exposed state. Further, the control circuit controls light emission of the light emitting unit such that light emission luminance at the start (t_es) of the exposure period increases as the exposure period of the image pickup element is shortened.