A method and device for drilling holes into a mantle of a cylinder used in a paper machine are disclosed. The drilling device includes a base frame and a spindle box displaceable on support of the base frame towards a cylinder mantle to be machined. The spindle box includes a number of drill bits and a drive motor arranged to move the spindle box to produce a feed movement for the drill bits. In the spindle box, a second motor is arranged to rotate the drill bits simultaneously. The rotating drive of the drill bits is obtained by means of the second motor which rotates a drive belt arranged to pass via drive pulleys of the drill bits so that the drive pulleys and drill bits are rotated. Each drill bit comprises a horizontally displaceable slide frame. Coupling devices are arranged between each displaceable slide frame and the spindle box, by means of which each slide frame can be locked in the desired horizontal position so as to adjust the positions of the drill bits.