An image pickup apparatus 12 includes a first camera 22 and a second camera 24. The cameras pick up an image of a target at the same timing and at the same frame rate from left and right positions spaced by a known distance from each other. Picked up frame images are converted into image data of a predetermined plurality of resolutions. An input information acquisition section 26 of an information processing apparatus 14 acquires an instruction input from a user. A position information production section 28 approximately estimates a region of the target or a region which involves some movement on an image of a low resolution and a wide range from within stereo image data as a target region and carries out stereo matching only in regard to the region on an image of a high resolution to specify a three-dimensional position of the target. An output information production section 32 carries out a necessary process based on the position of the target to produce output information. A communication section 30 carries out request for and acquisition of image data to and from the image pickup apparatus 12.