cover 10 remains closed by both the hook 29 and the claw 30 which cooperate with each other the lock spring 31 urges the claw 30 toward the hook 29 so that the claw 30 engages the hook 29 when the cover 10 is closed the claw 30 comprises an elastic locking arm 32 when the cover 10 is opened as a result of the disengagement of the claw 30 from the hook 29 the arm 32 engages a portion 33 of the camera body and the lock spring 31 prevents the claw 30 from returning to the position in which the claw 30 engages the hook 29 when the cover 10 is closed the arm 32 is pressed downward by an unlocking rib 34 formed on the cover 10 so that the arm 32 is disengaged from the portion 33 and the lock spring 31 allows the claw 30 to return to the position in which the claw 30 engages the hook 29 the claw 30 is integrally formed with a button 35 shown in fig4 mounted on the bottom surface of the camera body the claw 30 and the hook are disengaged from each other when the button 35 is operated by the photographer the movement of the claw 30 in the unlocking direction is restrained by a gravity operated lever 36 when the camera body is held for a normal horizontal format the gravity operation lever 36 is curved like a boomerang as shown in fig6 a weight 37 is mounted on one end of the gravity operated lever 36 so that one end drops by.