Monocular head-mounted displays (HMD) are expected as a core device for ubiquitous computing. However, monocular HMD can decrease the visibility by environment light. High luminance environment light makes high contrast between the environment and images presented by monocular HMD. This situation causes perceptional lost of the images. In this study, the authors examined a LCD backlight control method for the visibility of monocular HMD in various light situations. Four kinds of backlight control patterns were obtained by a psychophysical measurement, and the validity was also subjectively evaluated. This paper reports the results of the evaluation and discusses on the suitable backlight control in terms of human factors.