1. An object detecting system for a vehicle, comprising: a distance sensor mounted on the vehicle and capable of detecting a distance between the subject vehicle and the object, which is located ahead of the subject vehicle, along longitudinal and lateral directions of the subject vehicle, based on transmission of a signal toward the object, which is ahead of the subject vehicle, and reception of a reflected signal from the object, so as to detect the object based on output data from the distance sensor; a coordinate developing means for associating said output data from said distance sensor on XY coordinates having a Y-axis indicative of a longitudinal direction and an X axis indicative of a lateral direction with respect to the subject vehicle; a cell dividing and counting means for dividing said XY coordinates in directions of the X and Y axes at predetermined distances into a plurality of cells of equal size, for counting a number of the output data located in each of the cells and for outputting the XY coordinates and the number of the data for every cell as cell information; and an object discerning means for assigning same identifiers to cells which are adjacent to one another and include therein data on said object, based on said cell information output from said cell dividing means and for determining X and Y coordinates of the barycentric positions for every identifier by the following equations: EQU X=(X1.multidot.N1+X2.multidot.N2+. .. +Xn.multidot.Nn)/N EQU Y=(Y1.multidot.N1+Y2.multidot.N2+. .. +Yn.multidot.Nn)/N wherein X1, X2,. .. Xn denote X coordinates of cells in which data on said object are present, Y1, Y2,. .. Yn denote Y coordinates of said cells, N1, N2,. .. Nn denote the number of data in each cell, and N denotes the sum of the number of data present in the cells.