1. A measuring system for measuring light generated from a luminescent or fluorescent substance included in a liquid to be measured, or radiation included in the liquid to be measured, comprising: a separating device for separating the liquid to be measured; an imager forming an image of the separated liquid; and a boundary calculating device for determining boundaries of the separated liquid in the image, wherein: the measuring system measures the light or the radiation from the separated liquid within the determined boundaries, respectively; the separating device is a flat plate having grooves of a predetermined size, the liquid being in one of the grooves in which the liquid is separated; an edge enhancing device is provided for enhancing shading differences in the image of the separated liquid in the flat plate, the shading differences being treated as edges; a flow path position extracting device is provided for extracting, based on design information on the grooves having the predetermined size in the flat plate, and the flat plate, positions of the grooves by adjusting positions of pixels of the edges in the image; and the boundary calculating device determines the boundaries based on the pixels of the edges in the image comprising a detecting device for simultaneously and two-dimensionally detecting the light or radiation included in the liquid to be measured to obtain two-dimensional image information of the light or radiation, and a superimposition processing device for carrying out a superimposition process to superimpose the image of the separated liquid in the separating device picked up by the image pickup device and a distribution image of the two-dimensional image information obtained by the detecting device, wherein, based on areas of the liquid divided by the boundary calculating device, and areas in the distribution image superimposed thereon, information on the light or radiation in these areas is obtained; wherein the liquid to be measured is blood including radiation, the separating device carries out plasma separation which centrifuges and separates the blood into plasma and blood cell, and the boundary calculating device determines boundaries between plasma and blood cell, the detecting device simultaneously and two-dimensionally detects the radiation included in the blood to obtain two-dimensional image information of the radiation, the superimposition processing device carries out a superimposition process to superimpose the image resulting from the plasma separation and the distribution image of the two-dimensional image information obtained by the detecting device, and based on the plasma and blood cell divided by the boundary calculating device and the plasma and blood cell in the distribution image superimposed thereon, a radioactive concentration is determined for each of the plasma and blood cell.