A system for displaying an image of a virtual space on a display obtains detection data from position detection sensors, the position detection sensors including a position detection sensor attached to a user. The system calculates a distance between a pair of the position detection sensors based on the detection data, and sets, based on the distance, a boundary for determining a motion of the user. The system determines, when the motion of the user occurs, whether a positional relationship between one of the position detection sensors and the boundary satisfies a condition, and, responsive to the positional relationship satisfying the condition, executes an action corresponding to the motion of the user in the virtual space.