An apparatus for monitoring a surrounding environment of a vehicle, comprising: a sensor unit comprising a plurality of detection sensors for detecting an object outside a vehicle according to a frame at a predefined period; and a control unit configured to extract a stationary object from among the outside objects detected by the sensor unit by using behavior information of the vehicle, to map the extracted stationary object to a preset grid map, to add occupancy information to each of grids constituting the grid map depending on whether the mapping is performed, to calculate an occupancy probability parameter, indicative of a probability that the stationary object will be located on each of the grids of the grid map, from the occupancy information added to the grid in the grid map in a plurality of frames to be monitored, and to monitor the surrounding environment of the vehicle by specifying a grid on which the stationary object is located in the grid map, based on the calculated occupancy probability parameter while recognizing a free space around the vehicle using the specified grid, wherein the control unit is further configured to: determine a peak grid with a maximum occupancy probability parameter among the grids in the grid map for the plurality of frames to be monitored, and determine that the stationary object is located on the peak grid when the occupancy probability parameter of the peak grid is equal to or greater than a threshold value defined for the peak grid. a sensor unit comprising a plurality of detection sensors for detecting an object outside a vehicle according to a frame at a predefined period; and a control unit configured to extract a stationary object from among the outside objects detected by the sensor unit by using behavior information of the vehicle, to map the extracted stationary object to a preset grid map, to add occupancy information to each of grids constituting the grid map depending on whether the mapping is performed, to calculate an occupancy probability parameter, indicative of a probability that the stationary object will be located on each of the grids of the grid map, from the occupancy information added to the grid in the grid map in a plurality of frames to be monitored, and to monitor the surrounding environment of the vehicle by specifying a grid on which the stationary object is located in the grid map, based on the calculated occupancy probability parameter while recognizing a free space around the vehicle using the specified grid, wherein the control unit is further configured to: determine a peak grid with a maximum occupancy probability parameter among the grids in the grid map for the plurality of frames to be monitored, and determine that the stationary object is located on the peak grid when the occupancy probability parameter of the peak grid is equal to or greater than a threshold value defined for the peak grid. determine a peak grid with a maximum occupancy probability parameter among the grids in the grid map for the plurality of frames to be monitored, and determine that the stationary object is located on the peak grid when the occupancy probability parameter of the peak grid is equal to or greater than a threshold value defined for the peak grid.