A glass breakage detecting sensor includes a strain detecting portion by which breakage of a window glass, which is provided at a door of a vehicle, is detected based on changes of an amount of strain, and an attaching portion attached to at least one of an opening and closing mechanism, which freely movably supports the window glass, and an inner panel to which the opening and closing mechanism is arranged within the door, the opening and closing mechanism and the inner panel functioning as an attached portion.