An apparatus for controlling operation of an autonomously navigating utility vehicle equipped with a prime mover to travel about a working area delineated by a boundary line in order to perform work autonomously, comprising: a map generating unit that generates a working area map of the working area comprised of an array of a plurality of cells; a position detector (55, 51) that detects a first position of the vehicle in the working area map and a second position of the vehicle with respect to the boundary line of the working area; a memory unit that counts and memorizes a number of times n the vehicle passes over each of the cells based on the first position of the vehicle detected by the position detector (55, 51); a target cell setting unit that selects one of the cells based on the counted number n memorized in the memory unit and sets the selected one as a target cell; and a travel controlling unit that detects whether the vehicle has reached the boundary line based on the second position of the vehicle detected by the position detector (55, 51), and controls operation of the prime mover to make the vehicle travel about the working area until the vehicle is detected to have reached the boundary line; and to make the vehicle turn toward the target cell set by the target cell setting unit and then travel straight forward when the vehicle is detected to have reached the boundary line, characterized in that the target cell setting unit calculates an average value of the counted number n by dividing a sum of the counted numbers n of the cells by a total number of cells; and sets one of the cells as the target cell whose counted number n memorized in the memory unit is smaller than the average value by a predetermined value, wherein, if two, first and second, cells (210a and 210b) both satisfy the condition of having the counted number n smaller than the average value by the predetermined value and the counted number n of first cell is smaller than the counted number n of the second cell, and the vehicle cannot travel in the direction of the first cell because the boundary line is present between the vehicle and the first cell, the target cell setting unit excludes the first cell as the target cell candidate and sets the second cell as the target cell. a map generating unit that generates a working area map of the working area comprised of an array of a plurality of cells; a position detector (55, 51) that detects a first position of the vehicle in the working area map and a second position of the vehicle with respect to the boundary line of the working area; a memory unit that counts and memorizes a number of times n the vehicle passes over each of the cells based on the first position of the vehicle detected by the position detector (55, 51); a target cell setting unit that selects one of the cells based on the counted number n memorized in the memory unit and sets the selected one as a target cell; and a travel controlling unit that detects whether the vehicle has reached the boundary line based on the second position of the vehicle detected by the position detector (55, 51), and controls operation of the prime mover to make the vehicle travel about the working area until the vehicle is detected to have reached the boundary line; and to make the vehicle turn toward the target cell set by the target cell setting unit and then travel straight forward when the vehicle is detected to have reached the boundary line, characterized in that the target cell setting unit calculates an average value of the counted number n by dividing a sum of the counted numbers n of the cells by a total number of cells; and sets one of the cells as the target cell whose counted number n memorized in the memory unit is smaller than the average value by a predetermined value, wherein, if two, first and second, cells (210a and 210b) both satisfy the condition of having the counted number n smaller than the average value by the predetermined value and the counted number n of first cell is smaller than the counted number n of the second cell, and the vehicle cannot travel in the direction of the first cell because the boundary line is present between the vehicle and the first cell, the target cell setting unit excludes the first cell as the target cell candidate and sets the second cell as the target cell.