A vehicular display device adjustment method including an imaging step of taking an image of the periphery of a vehicle by imaging element, an image storing step of temporarily storing in an image storing element peripheral image data based on the peripheral image of the vehicle taken by the imaging element, a setting step of setting an adjustment mode for adjusting the display state of display element, a display control step of giving priority to the peripheral image based on the peripheral image data stored in the memory over the peripheral image taken in the imaging step in accordance with the adjustment mode set and displaying on the display element the peripheral image based on the peripheral image data stored in the memory, and an adjustment step of adjusting the display state of the display element based on the peripheral image.