An apparatus for controlling operation of an autonomously navigating utility vehicle equipped with a prime mover powered by a battery to travel about a working area delineated beforehand in order to perform work autonomously, the apparatus comprising: a mode switching unit that is configured to switch operating mode between work mode for making the vehicle autonomously travel on a travel locus and perform work in the working area and return mode for making the vehicle return on a return route to a charging device located at the working area in order to charge the battery; a position detector (52, 57) that is configured to detect position of the vehicle on a map of the working area that is divided into an array of a plurality of cells; a cell memorizing unit that is configured to identify a series of travel locus cells on which the vehicle has traveled in the work mode from among the plurality of travel locus cells based on the position of the vehicle detected by the position detector, assign successively incrementing cell numbers (n) to the series of travel locus cells, and memorize the series of travel locus cells in association with the assigned cell numbers (n), the series of travel locus cells starting from a starting cell at a location of the charging device to a current cell at which the position of the vehicle is detected by the position detector; a cell selecting unit that is configured to successively select a return locus cell to which the vehicle is to move from the current cell from among the series of travel locus cells memorized by the cell memorizing unit, when the operating mode is switched from the work mode to the return mode by the mode switching unit, the return locus cell being adjacent to the current cell, a cell number of the return locus cell being smaller than a cell number of the current cell; and a travel controlling unit that is configured to control operation of the prime mover to make the vehicle travel to the return locus cell successively selected by the cell selecting unit to return to the charging device on the return route, characterized in that when the vehicle in the work mode travels a loop with the travel locus forming an intersection on one travel locus cell of the series of travel locus cells that have already been assigned cell numbers, the cell memorizing unit deletes the cell numbers that are larger than the cell number of the travel locus cell at the intersection that has already been assigned successively incrementing cell number thus deleting the loop in the return mode, and resumes assigning cell numbers starting from the cell number of the travel locus cell at the intersection such that interconnected return locus cells selected from the travel locus cells have no intersection or crossing. a mode switching unit that is configured to switch operating mode between work mode for making the vehicle autonomously travel on a travel locus and perform work in the working area and return mode for making the vehicle return on a return route to a charging device located at the working area in order to charge the battery; a position detector (52, 57) that is configured to detect position of the vehicle on a map of the working area that is divided into an array of a plurality of cells; a cell memorizing unit that is configured to identify a series of travel locus cells on which the vehicle has traveled in the work mode from among the plurality of travel locus cells based on the position of the vehicle detected by the position detector, assign successively incrementing cell numbers (n) to the series of travel locus cells, and memorize the series of travel locus cells in association with the assigned cell numbers (n), the series of travel locus cells starting from a starting cell at a location of the charging device to a current cell at which the position of the vehicle is detected by the position detector; a cell selecting unit that is configured to successively select a return locus cell to which the vehicle is to move from the current cell from among the series of travel locus cells memorized by the cell memorizing unit, when the operating mode is switched from the work mode to the return mode by the mode switching unit, the return locus cell being adjacent to the current cell, a cell number of the return locus cell being smaller than a cell number of the current cell; and a travel controlling unit that is configured to control operation of the prime mover to make the vehicle travel to the return locus cell successively selected by the cell selecting unit to return to the charging device on the return route, characterized in that when the vehicle in the work mode travels a loop with the travel locus forming an intersection on one travel locus cell of the series of travel locus cells that have already been assigned cell numbers, the cell memorizing unit deletes the cell numbers that are larger than the cell number of the travel locus cell at the intersection that has already been assigned successively incrementing cell number thus deleting the loop in the return mode, and resumes assigning cell numbers starting from the cell number of the travel locus cell at the intersection such that interconnected return locus cells selected from the travel locus cells have no intersection or crossing.