Parking assistance device

A parking assistance device comprising:

• a distance sensor for transmitting a detection wave laterally with respect to a host vehicle and receiving a reflected wave of the detection wave during travelling of the host vehicle;
• and
• processing circuitry to
• calculate reflection points indicating a position at which the detection wave is reflected;
• group the reflection points;
• calculate a parking space pitch indicating a width of a parking space by using periodicity of a shape included in a reflection point group set in the grouping;
• set a parking target area which is a target of perpendicular parking by the host vehicle;
• and
• guide the host vehicle to the parking target area on a basis of the parking space pitch, wherein
• the processing circuitry is configured to calculate an autocorrelation function on a curve connecting the reflection points included in the reflection point group, and calculate the parking space pitch on a basis of an interval between peak points on a characteristic curve indicating the autocorrelation function.