A memory of a photographing field angle calculation apparatus has stored therein the position of each point captured by an imaging system as three coordinate values in horizontal, vertical, and depth directions when a photography space is photographed by the imaging system. A usage pixel value extraction means selects a plurality of points located in end portions in the horizontal direction of a range captured by the imaging system from those stored in the memory based on the vertical coordinate value, and extracts the horizontal and depth coordinate values of each of the selected points. A field angle calculation means calculates a horizontal photographing field angle when the photography space is photographed using the extracted horizontal and depth coordinate values.