1. A forward object estimation apparatus for a vehicle to detect a forward object and preventing collision between the vehicle and the forward object, the forward object estimation apparatus comprising: a radar unit configured to detect a distance, a velocity and an orientation of the forward object using radar waves, the radar unit outputting a distance observation, a velocity observation and an orientation observation regarding the forward object; a drive assist electronic control unit (ECU) configured to receive the distance information, the velocity information and the orientation information from the radar unit, the drive assist ECU comprising: a displacement calculator configured to use the velocity observation at each of times within a predetermined period to calculate, for each of the times, a temporal integral value of the velocity observations from a start time of the predetermined period to a corresponding one of the times, the temporal integral value calculated for each of the times serving as a displacement observation of the forward target within the start time to a corresponding one of the times; and a distance estimator configured to: perform regression analysis using, as samples, the distance observations and the displacement observations at the respective times within the predetermined period, the regression analysis being based on the distance as an objective variable and the displacement as an explanatory variable; and estimate that a value of the distance upon a value of the displacement calculated in accordance with a regression equation based on the regression analysis being zero shows a value of the distance to the forward object at the start time, and an output unit configured to output a target control signal based on the value of the distance to the forward object at the start time; and a controller target unit configured to receive the target control signal and perform a vehicle control to perform at least one of: preventing collision with the forward object based on the target control signal; and warning about the forward object based on the target control signal.