The purpose of this study is to clarify the characteristics of the gender-biased context shown in the geography textbook of middle-school. To achieve this goal, six social study textbooks were examined. Texts, illustrations, and pictures related to gender-prejudices and gender-related misunderstandings in the textbooks were analyzed quantitatively. Study was focused on four topics: i) Which gender - male or female - is appeared more frequently in the texts, illustrations, and pictures in the school textbooks? ii) Which gender play a key role? iii) How the prejudice about the social role by gender is presented? iv) Are some textbooks more gender-biased?; and is this related to the gender of the author? Findings are as follows: i) Man appeared more frequently than woman in texts, illustration, and pictures in the school textbooks. The illustrations are more gender-biased, favouring male. ii) Most textbooks show gender-stereotyped roles and activities; man plays progressive, aggressive, and diverse roles. Woman, however, plays an inactive and relatively insignificant role in social activity. iii) The gender-proportion of the author is bias in favour of male. Female authors form only 12 percent. Four of the six textbooks, in which woman teachers are not participated, are more gender-biased than the others. These results show that gender-prejudices exist even in the geography studies which are known, so far, as fact-oriented and value-free. To remedy this gender-bias, it is suggested that woman\'s participation in the development of curriculum and school textbooks should be increased.