1. A semiconductor failure analysis apparatus for analyzing a failure of a semiconductor device, using an observed image thereof, comprising: inspection information acquiring means for acquiring inspection information containing at least a pattern image being a normal observed image of the semiconductor device obtained by image acquiring means in a semiconductor inspection apparatus, and a failure observed image containing reaction information arising from a failure obtained by conducting an inspection of the failure by the semiconductor inspection apparatus, as the observed image; layout information acquiring means for acquiring layout information containing a layout image generated from design information of the semiconductor device; failure analyzing means for analyzing a failure of the semiconductor device with reference to the observed image; and information display controlling means for letting display means display information about an analysis of the failure of the semiconductor device, wherein the information display controlling means has superimposed image generating means for generating a superimposed image in which the layout image is superimposed on the pattern image, and the failure observed image is further superimposed on the pattern image and the layout image, as an image of the semiconductor device to be displayed by the display means, first transmittance setting means for variably setting a first transmittance of the layout image relative to the pattern image, corresponding to a superimposing ratio between the layout image and the pattern image, in the superimposed image, and second transmittance setting means for variably setting a second transmittance of the failure observed image relative to the pattern image and the layout image, corresponding to a superimposing ratio of the failure observed image, in the superimposed image, wherein the superimposed image generating means generates the superimposed image by superimposing the layout image on the pattern image and further superimposing the failure observed image on the pattern image and the layout image by using the superimposing ratios determined from the first transmittance and the second transmittance variably set by the first transmittance setting means and the second transmittance setting means, and wherein the information display controlling means has analysis screen generating means for generating an analysis screen having an image display region for displaying the superimposed image generated by the superimposed image generating means, and a display adjustment region provided with a first transmittance setting part used for setting of the first transmittance in the first transmittance setting means and a second transmittance setting part used for setting of the second transmittance in the second transmittance setting means, as a screen to be displayed by the display means.