The sucking grasp, for example, the silicon or the rubber sucker has been used widely to handle the parts in various stages of the automated process. But in order to use the sucking grasp more widely, it is necessary to develop the other type of sucking unit. In this paper, we examined the distribution of the vacuum pressure in the contact surface and estimated the adsorptive force from the vacuum pressure, the area of the contact surface, the area or the number of sucking holes, and a gap or a roughness of surface under the contact condition that the flat surface of the sucking unit sucked up the flat surface of an object. The vacuum pressure in the contact surface decreased exponentially, as the distance from the edge of the sucking hole became long. And the adsorptive force was estimated from the equation Y=1.147.P.S.(S/M)(-0.6) in the case of one sucking hole. It is necessary to consider the interaction between two sucking holes which were only separated by a very close distance to estimate the adsorptive force in case of many sucking holes. The adsorptive force became weak, as the gap