The invention relates to an underwater drilling device and to a method for procuring drill cores of a bed of a body of water, wherein an underwater drilling device with a base frame is lowered in a body of water and placed on a bed of a body of water. A drill string consisting of at least one tubular drill string element is drilled out into the bed of the body of water in a first drilling step with a drill drive, with a drill core being formed in a receptacle in the tubular drill string element and being received in a core barrel in the drill string element. According to the invention, the drill core is enclosed in pressure-tight manner in a receiving container on the basic cradle under water.