An occupant monitoring device for a vehicle is configured to monitor an occupant sitting on a seat provided in a vehicle and includes a light projector, an imaging device, and a processor. The light projector is configured to project light toward the occupant sitting on the seat. The imaging device is configured to capture an image of the occupant sitting on the seat. The processor is configured to control the light projector and the imaging device to capture the image of the occupant sitting on the seat. In a case where a collision of the vehicle is predicted, the imaging device captures the image at a higher speed than in a normal case where a collision of the vehicle is not predicted.