An apparatus for controlling operation of an autonomously navigating turnable utility vehicle equipped with a body and a prime mover mounted on the body to make the vehicle travel about a working area delineated by a boundary wire laid thereat in order to work autonomously, the working area including a first area and a second area (AR2) connected to the first area, a distance between mutually facing segments (2a, 2b) of the boundary wire in the first area being equal to or less than a predetermined value (Wa) over a predetermined length (La), a distance (W2) between mutually facing segments of the boundary wire in the second area (AR2) being greater than the predetermined value (Wa), having: a magnetic field strength detector installed on the body to detect a magnetic field strength generated by electric current passing through the boundary wire; and a travel controlling unit configured to control the prime mover to make the vehicle turn and travel straight forward every time the vehicle traveling in the working area reaches the boundary wire, based on the magnetic field strength detected by the magnetic field strength detector; and a first area determining unit configured to determine that the vehicle travels in the first area when the magnetic field strength detected by the magnetic field strength detector is greater than a first threshold value (Ha) predefined based on a minimum value of the magnetic field strength in the first area for a first time period from a first turn to a second turn of the vehicle, or when the magnetic field strength detected by the magnetic field strength detector is greater than a second threshold value (Hb) for a predetermined time period (Δt) after the first turn characterized in that both of the first threshold value (Ha) and the second threshold value (Hb) are set to values smaller than minimum values of the magnetic field strength in the first area and greater than maximum values of the magnetic field strength in the second area (AR2). a magnetic field strength detector installed on the body to detect a magnetic field strength generated by electric current passing through the boundary wire; and a travel controlling unit configured to control the prime mover to make the vehicle turn and travel straight forward every time the vehicle traveling in the working area reaches the boundary wire, based on the magnetic field strength detected by the magnetic field strength detector; and a first area determining unit configured to determine that the vehicle travels in the first area when the magnetic field strength detected by the magnetic field strength detector is greater than a first threshold value (Ha) predefined based on a minimum value of the magnetic field strength in the first area for a first time period from a first turn to a second turn of the vehicle, or when the magnetic field strength detected by the magnetic field strength detector is greater than a second threshold value (Hb) for a predetermined time period (Δt) after the first turn characterized in that both of the first threshold value (Ha) and the second threshold value (Hb) are set to values smaller than minimum values of the magnetic field strength in the first area and greater than maximum values of the magnetic field strength in the second area (AR2).