A driving assistance device, comprising: a preceding vehicle detection portion that detects a preceding vehicle in front of a host vehicle in which the driving assistance device is disposed; a speed control portion that controls a speed adjustment of the host vehicle to make an inter-vehicle distance between the host vehicle and the preceding vehicle become a target inter-vehicle distance; a preceding vehicle travel trajectory acquisition portion that acquires a travel trajectory of the preceding vehicle; an entering vehicle detection portion that detects an entering vehicle which enters between the host vehicle and the preceding vehicle; an entering vehicle travel trajectory acquisition portion that acquires a travel trajectory of the entering vehicle detected by the entering vehicle detection portion; a target trajectory setting portion that sets a target travel trajectory of the host vehicle based on at least one of the travel trajectory of the preceding vehicle and the travel trajectory of the entering vehicle; a steering control portion that controls an adjustment of a steer amount of the host vehicle based on the target travel trajectory; and a location determination portion that determines a location where a deviation amount between the travel trajectory of the entering vehicle and the travel trajectory of the preceding vehicle becomes a predetermined value or below, wherein the speed control portion sets the entering vehicle as the preceding vehicle of the speed control portion when the entering vehicle is detected by the entering vehicle detection portion, and characterized in that the target trajectory setting portion sets the target travel trajectory of the host vehicle based on the travel trajectory of the preceding vehicle before entering of the entering vehicle at least until reaching the location determined by the location determination portion after the speed control portion sets the entering vehicle as the preceding vehicle, and sets the target travel trajectory of the host vehicle based on the travel trajectory of the entering vehicle after the location determined by the location determination portion. a preceding vehicle detection portion that detects a preceding vehicle in front of a host vehicle in which the driving assistance device is disposed; a speed control portion that controls a speed adjustment of the host vehicle to make an inter-vehicle distance between the host vehicle and the preceding vehicle become a target inter-vehicle distance; a preceding vehicle travel trajectory acquisition portion that acquires a travel trajectory of the preceding vehicle; an entering vehicle detection portion that detects an entering vehicle which enters between the host vehicle and the preceding vehicle; an entering vehicle travel trajectory acquisition portion that acquires a travel trajectory of the entering vehicle detected by the entering vehicle detection portion; a target trajectory setting portion that sets a target travel trajectory of the host vehicle based on at least one of the travel trajectory of the preceding vehicle and the travel trajectory of the entering vehicle; a steering control portion that controls an adjustment of a steer amount of the host vehicle based on the target travel trajectory; and a location determination portion that determines a location where a deviation amount between the travel trajectory of the entering vehicle and the travel trajectory of the preceding vehicle becomes a predetermined value or below, wherein the speed control portion sets the entering vehicle as the preceding vehicle of the speed control portion when the entering vehicle is detected by the entering vehicle detection portion, and characterized in that the target trajectory setting portion sets the target travel trajectory of the host vehicle based on the travel trajectory of the preceding vehicle before entering of the entering vehicle at least until reaching the location determined by the location determination portion after the speed control portion sets the entering vehicle as the preceding vehicle, and sets the target travel trajectory of the host vehicle based on the travel trajectory of the entering vehicle after the location determined by the location determination portion.