Disclosed is a parking assisting device, including: a camera for capturing an image behind a vehicle; a display provided to a dashboard of the vehicle; passage width measurement device that measures a width of a passage; and a controller for displaying the image captured with the camera on the display. Also disclosed is a device for calculating an initial stopping position required for parking the vehicle in-parallel into a target parking space perpendicular to the passage on the basis of the passage width measured, with the passage width measurement device, to superimpose on a screen of the display a displayed image for guidance used for guiding the vehicle to the initial stopping position.