Abstract: A firm closure and locking device to firmly close and lock a vent window pivotally mounted and adjacent to a rigid member. The device has a body portion configured in a U-shape which fits over the edge of the vent window adjacent to the rigid member. A locking arm is pivotally mounted to the body onto a pivot element, preferably a screw-like member projecting from the body. A pressure-bearing device, such as a handle with an internal threaded receptacle portion is threadedly engaged onto the screw-like member. The handle is rotated upon the screw-like member to advance it inwards towards the body, thereby applying pressure against the locking arm intermediate the handle and the body of the locking device. When the U-shaped portion of the body is fitted over the edge of the vent window adjacent the rigid member and no pressure is applied against the locking arm, the locking arm is free to rotate about the screw-like member until it abuts against the side of the adjacent rigid member.