PURPOSE: To obtain window structure reducing heat load during the year and capable of contributing to energy conservation.

CONSTITUTION: The body concealing sections 7 of a building are adjoined to the upper and lower sections of the window opening section 8 of the building, and guide members 5 are mounted on both left and right sections of these window opening section 8 and upper and lower body concealing sections 7 so as to connect the window opening section 8 and the body concealing sections 7. A first window panel 1 and a second window panel 2 mutually adjoined so as to form the same surface and unified by connecting members 21 are slid vertically through the guide members 5.