A monitoring system, comprising: a camera that obtains face images by successively imaging a face of an occupant in a vehicle; a pair of a right-side light source and a left-side light source that irradiates the face of the occupant with light, the pair of the right-side light source and the left-side light source being disposed in a horizontal direction with the camera interposed between the right-side light source and the left-side light source when the camera is viewed from a vertical direction; a lighting controller that controls the right-side light source and the left-side light source; and a controller that determines a visual line state including opening/closing of eyes of the occupant by using a plurality of the face images (31, 33, 39, 40) obtained with the camera, and gives warning to the occupant based on a result of the determination, characterized by a face direction determination unit that determines the direction of the face of the occupant by using the face images; and in that when the direction of the face of the occupant is determined to be directly forward when viewed from the camera, the lighting controller alternately turns on the right-side light source and the left-side light source for each imaging by the camera, the camera obtains each of a first face image that is imaged in accordance with lighting of the right-side light source and a second face image that is imaged in accordance with lighting of the left-side light source, and the controller determines the visual line state using the first face image and the second face image, when the direction of the face of the occupant is not determined to be directly forward when viewed from the camera, the lighting controller turns only the left-side light source on when the face of the occupant is determined to be rotated to the right direction when viewed from the camera, and turns only the right-side light source on when the face of the occupant is determined to be rotated to the left direction when viewed from the camera, the camera obtains a face image for determination that is imaged in accordance with lighting of the right-side light source or a face image for determination that is imaged in accordance with lighting of the left-side light source, and the controller determines the visual line state using the respective face image (39, 40) for determination. a camera that obtains face images by successively imaging a face of an occupant in a vehicle; a pair of a right-side light source and a left-side light source that irradiates the face of the occupant with light, the pair of the right-side light source and the left-side light source being disposed in a horizontal direction with the camera interposed between the right-side light source and the left-side light source when the camera is viewed from a vertical direction; a lighting controller that controls the right-side light source and the left-side light source; and a controller that determines a visual line state including opening/closing of eyes of the occupant by using a plurality of the face images (31, 33, 39, 40) obtained with the camera, and gives warning to the occupant based on a result of the determination, characterized by a face direction determination unit that determines the direction of the face of the occupant by using the face images; and in that when the direction of the face of the occupant is determined to be directly forward when viewed from the camera, the lighting controller alternately turns on the right-side light source and the left-side light source for each imaging by the camera, the camera obtains each of a first face image that is imaged in accordance with lighting of the right-side light source and a second face image that is imaged in accordance with lighting of the left-side light source, and the controller determines the visual line state using the first face image and the second face image, when the direction of the face of the occupant is not determined to be directly forward when viewed from the camera, the lighting controller turns only the left-side light source on when the face of the occupant is determined to be rotated to the right direction when viewed from the camera, and turns only the right-side light source on when the face of the occupant is determined to be rotated to the left direction when viewed from the camera, the camera obtains a face image for determination that is imaged in accordance with lighting of the right-side light source or a face image for determination that is imaged in accordance with lighting of the left-side light source, and the controller determines the visual line state using the respective face image (39, 40) for determination.