A parking assistance device comprising: an emission unit configured to emit ultrasonic waves in at least an outward lateral direction of a vehicle and in an interior of a conic surface having a predetermined angle with respect to a horizontal reference axis; a reception unit configured to receive reflection waves from an object reflecting the emitted ultrasonic waves; and an object determination unit configured to, based on a change in a detection state of an object that exists on a far side of a target parking region in which the vehicle is to be parked, the detection state having been specified based on reflection wave data obtained using the reflection waves from the object, determine a feature relating to the height of the object as the vehicle enters the target parking region, the object determination unit including a storage unit configured to store the reflection wave data each time the vehicle moves a predetermined distance, characterized in that the detection state is a detection frequency at a time when the reflection wave data stored in the storage unit is mapped in a two-dimensional map and the reflection wave data has been grouped based on a distribution state of the mapped reflection wave data, the detection frequency being calculated based on the grouped reflection wave data, and the object determination unit generates the two-dimensional map from the reflection wave data stored each time the vehicle moves the predetermined distance, and determines whether the object is a high height object or a low height object based on trends of increasing and decreasing in the detection frequency. an emission unit configured to emit ultrasonic waves in at least an outward lateral direction of a vehicle and in an interior of a conic surface having a predetermined angle with respect to a horizontal reference axis; a reception unit configured to receive reflection waves from an object reflecting the emitted ultrasonic waves; and an object determination unit configured to, based on a change in a detection state of an object that exists on a far side of a target parking region in which the vehicle is to be parked, the detection state having been specified based on reflection wave data obtained using the reflection waves from the object, determine a feature relating to the height of the object as the vehicle enters the target parking region, the object determination unit including a storage unit configured to store the reflection wave data each time the vehicle moves a predetermined distance, characterized in that the detection state is a detection frequency at a time when the reflection wave data stored in the storage unit is mapped in a two-dimensional map and the reflection wave data has been grouped based on a distribution state of the mapped reflection wave data, the detection frequency being calculated based on the grouped reflection wave data, and the object determination unit generates the two-dimensional map from the reflection wave data stored each time the vehicle moves the predetermined distance, and determines whether the object is a high height object or a low height object based on trends of increasing and decreasing in the detection frequency.