An automatic opening and closing system for opening and closing a window by automatically locking and unlocking a lock section of the window and by using a sensor, with a lock locking and unlocking mechanism for locking and unlocking a window of a building Apprising a stand fitted into a hole opened in one window frame, a lock section constituted by a lock body provided at this stand, a lock piece engaging with the lock section provided at the remaining frame, and a first controller for moving the lock piece, with the lock locking and unlocking mechanism actuated by operation of the first controller so as to lock and unlock the window, and the window opening and closing mechanism for opening and/or closing the window comprising a fitting lug body fitted to the frame, a stopping lug provided at the fitting lug body, a drive section such as a motor etc. capable of forward and reverse motion provided at the fitting lug body, a drive section body axially installed at the drive section and coming into contact with the window frame, and a second controller for actuating the drive section, with the drive section being actuated by operation of the second controller so as to open and close the window.