The aim of the present research is to investigate individual differences in the strength and the spatial range of the visual attention. We measured detection sensitivity of a visual target in the conditions with attention and without attention. The double task and the single task paradigms were adopted in the main experiment. In the double task condition the observer responded only when the central task was correctly performed. It was possible to estimate the sensitivity change by comparing the results in these twoconditions. The Gabor pattern was uses as a stimulus and its spatial frequency was set at 0.5,1,2,4,8,and 16 cpd. Ten observers participated in this experiment. In the main experiment an apparatus was newly built which consisted of 6 mirrors and two monitors to make the viewing distance long enough to produce fine gratings. It was possible to measure spatial contrast sensitivity with frequency by using this apparatus.The results show that the spatial contrast sensitivities were found to be lower with the central task than those without the central task for all observers, which means that when attention is not paid to the target area the detection sensitivity decreases. Clear individual differences exist in the spatial frequency characteristics of sensitivity reduction. These individual differences are categorized into four patterns. 1.Large sensitivity reduction, larger in high spatial frequencies, 2.Large sensitivity reduction, no spatial selectivity, 3.Small sensitivity reduction, larger in middle spatial frequencies, 4.Small sensitivity reduction, no spatial frequency selectivity.