An obstacle alert device is capable of indicating clearly presence of an obstacle approaching a vehicle to a driver, without impairing visibility of a peripheral situation of the vehicle. The device includes a photographed image acquisition section acquiring a photographed image photographing a scene in the periphery of the vehicle, a photographed-image-of-interest generation section generating a photographed image of interest based on the photographed image, a masked region setting section setting a masked region making undisplayed at least a portion of the scene of the vehicle periphery in the photographed image of interest, an object presence determination section determining whether an object is present or not in an outside region outside the photographed image of interest, and a masked-region highlighted-displaying section causing the masked region to be displayed with highlight when an object in the outside region has entered a region corresponding to the photographed image of interest.