A periphery monitoring device includes: an image acquisition unit acquiring an image obtained from an imaging unit imaging a situation surrounding a towing vehicle to which a towed vehicle is connectable; a projection plane acquisition unit acquiring a three-dimensional virtual projection plane onto which the image can be projected and which is provided with a side plane rising in a height direction from a grounding surface of the towing vehicle; a projection processing unit projecting the image onto the virtual projection plane; a viewpoint setting unit setting a viewpoint position and a gazing point position with respect to the virtual projection plane; an image display unit causing a display device to display an image obtained by viewing the gazing point position from the viewpoint position with respect to the virtual projection plane; and a determination unit determining whether or not the towed vehicle is connected to the towing vehicle.