Method for drilling and drilling apparatus

Drilling apparatus having a drilling device (1) that comprises a casing part (2), essentially inside of which there is at least during a drilling situation a drilling unit (3), in the drilling head (I) of which there are at least first drilling means (4) for drilling a center hole and second drilling means (5) for reaming of the center hole for the casing part (2) as well as flushing flow arrangement (6) for flushing of waste, being generated, such as for feeding of flushing medium for the drilling and for removal of drilling waste, being generated, essentially inside the casing part (2), whereby at least during the drilling situation the first drilling means (4) are coupled by a power transmitting and, in order to enable removal of the same from the hole, removable arrangement, such as a bayonet coupling or like, with the second drilling means (5), whereby the casing part (2) is arranged to be drawn into the hole to be drilled by means of the first and of the second drilling means, characterized in that inside a first frame part (4a), belonging to the first drilling means (4), is arranged a first transferring arrangement (X1) in order to transfer a feed flow (6a) of flushing medium, being carried out centrally, through internal drillings to the outer periphery of the first frame part (4a) and a second transferring arrangement (X2), in order to accomplish a so called reverse circulation of flushing medium, by leading a return flow (6b) through internal drillings from the drilling surface (pp2) of the first frame part (4a) into a space (z) between the first frame part (4a) and the casing part (2).