Disclosed are a window apparatus for obtaining a microscopic image of in vivo breast tissue and a method for using the window apparatus to obtain cell-level and molecular-level microscopic images of in vivo breast tissue while maintaining the biological environment of the in vivo breast tissue. In one embodiment, a window apparatus comprises a first chamber having a ring structure with an open window on the center, and a cover glass disposed on the upper part and breast tissue placed on the lower part; a second chamber having an opening window on the center coupled to the first chamber to support the breast tissue; and a chamber holder for fixing the first and second chambers having a tilting mount placing unit with the tilting mount placed to have the cover glass and an object lens of a confocal microscope system stay parallel to each other.