To provide a deep hole processing device capable of processing a highly accurate large diameter deep hole, by using a general purpose machine tool, without requiring processing of a pilot hole.

The deep hole processing device forms a hole by rotatably moving a main spindle 17 attached with a tool 8 in a portal machine toward a workpiece, and includes a bush 9 having a hole for guiding the rotational movement of the tool 8 and a bush holding part 11 arranged on a cross rail movable on a column in the portal finishing machine and holding the bush 9 at a predetermined distance to a main spindle head 1 attached with the main spindle 17, and is characterized in that a position to the workpiece of the bush 9 and pressure of pushing the bush 9 against the workpiece, can be controlled by the movement of the cross rail.