In at least one embodiment of this disclosure, footfalls are output at intervals of a time Ta in accordance with input for movement of a user A in the virtual space. Footfalls are output at intervals of a time Tb in accordance with input for movement of the user B in the virtual space. The computer updates the field-of-view image displayed on a head-mounted device, and further, outputs footfalls at intervals of time that is based on setting of the physical size of the user of the head-mounted device.