1. A range image sensor, comprising: a light source which emits intensity modulated light toward an object space according to a modulation signal of a specific frequency! a light detecting element with photosensitive units disposed to face said object space, each of the photosensitive units receiving light from said object space during an integration period shorter than one period of said specific frequency, and generating an electric charge in response to a quantity of light from the space! a sensor control stage which controls to synchronize each integration period of said photosensitive units with a specific phase of said modulation signal, and pick up each electric charge generated and integrated in said light detecting element from the light detecting element after a detection period corresponding to one or more periods of said specific frequency! and an image construction stage which calculates a distance value for each image element in a range image based on each electric charge picked up by said sensor control stage to construct the range image, said distance value representing, when at least a physical object is in said object space, distance up to the physical object! wherein ˆ said detection period includes different detection periods! and said image construction stage calculates a distance value for each image element in said range image based on each electric charge picked up after a specific detection period of said different detection periods by said sensor control stage, said specific detection period being one of one or more detection periods during which said light detecting element does not reach saturation, and being one detection period during which a value related to the quantity of light received from said object space becomes maximum of that of the one or more detection periods.