1. A drive assist apparatus in a vehicle, the driving assist apparatus having a prediction information acquisition section that successively acquires prediction information at a time point from an in-vehicle information detection portion, the prediction information being enabled to be transmitted via inter-vehicle communications, the drive assist apparatus comprising: a via-point prediction section to obtain a predicted via-point of the vehicle where the vehicle exists from a time point to a future time point on a basis of prediction information at the time point acquired by the prediction information acquisition section, the prediction information at the time point containing at least a position at which the vehicle exists at the time point; a difference determination section that, when the prediction information acquisition section newly acquires second prediction information at a second time point that is later than a first time point, obtains a difference between (i) a predicted via-point of the vehicle predicted at the second time point between the first time point to the future time point on a basis of first prediction information at the first time point, the first prediction information at the first time point being acquired at the first time point by the prediction information acquisition section and being already transmitted via the inter-vehicle communications and (ii) a position, at which the vehicle exists at the second time point, obtained on a basis of the second prediction information at the second time point, the difference determination section further determining whether the obtained difference is a predetermined value or more; and a transmission determination section that determines that the second prediction information newly acquired is transmitted when the difference determination section determines that the difference is the predetermined value or more, and determines that the second prediction information newly acquired is not transmitted when the difference determination section determines that the difference is not the predetermined value or more.