In a locking and unlocking apparatus of an engine hood door (120), a stay (130) is formed of a first arm and a second arm, with the stay being provided so as to fix a door of an engine hood in a fixed state. The first arm and the second arm are foldably connected to each other and pivotally connected to a frame (110) and a door respectively. The lock of the first arm is automatically locked by a locking piece of the second arm at a portion in which the first arm and the second arm are arranged on a straight line for thereby maintaining an opened state of the door. The lock is unlocked from the locking piece with the locking piece being pulled by operation of a lever which is connected with the locking piece through a wire from a remote site, so that the door is closed.