A vehicle surroundings monitoring device measures coordinates of an obstacle on a first coordinate system on the basis of a position of the vehicle at a first time point at which a transmission wave is output and a position of the vehicle at a second time point at which a reflected wave of the transmission wave is detected. The monitoring device writes, to a storage device, coordinates of the obstacle on a second coordinate system having a resolution lower than a resolution of the first coordinate system when power turn-off of the vehicle is detected. The monitoring device reads, from the storage device, the coordinates of the obstacle on the second coordinate system when power turn-on of the vehicle is detected. The monitoring device determines whether the vehicle and the obstacle come into contact with each other by using the coordinates of the obstacle read from the storage device.