A driving assistance device includes processing circuitry to acquire host vehicle information, receive mobile object information from a mobile object outside the host vehicle using wireless communication, determinate a right or left turn of the host vehicle based on the host vehicle information, obtain a prediction point by calculating a right or left turn point of the host vehicle based on the host vehicle information, determine whether or not the host vehicle collides with the mobile object using the host vehicle information, the mobile object information, and the prediction point, and perform driving assistance of the host vehicle based on a result of the collision determination. The processing circuitry obtains the prediction point by calculating, on a basis of a preset deceleration, a distance required for the speed of the host vehicle HV included in the host vehicle information to reach a target speed set in advance.