The present invention provides a colostomy bag. The colostomy bag comprises: a bag having a left gusset face that is folded between a front face and a back face, and a right gusset face that is folded between the front face and the back face, the bag being open at the upper side and sealed at the lower side and a contact body that has a substantially same width dimension as the width dimension of the bag, and has one surface in contact with the outer surface of the receiving bag and an opposite surface adapted to be in contact with a skin area around the anus. The contact body is folded in half with one side of the crease bonded to the front face of the bag such that the crease is laid along the upper side of the bag, whereas the other side of the crease is bonded to the back face of the bag so that the upper side of the bag is sealed with the contact body. Within a range of the contact body, a cut-out portion is then formed in the contact body and the bag so that the contact body can be opened at the crease side.
