To provide a cleaning device for parallel holes capable of rapidly cleaning the inner peripheral surfaces of parallel holes within a short time and capable of expecting the enhancement of cleaning work efficiency.

A cleaning device for parallel holes is equipped with a cleaning device main body 2 consisting of a pair of split rod elements 2a, 2b formed by spliting a rod element having a uniform cross section into two along a vertical cross section inclined with respect to a center axial line L and setting one of them to a fixed side and the other one of them to a movable side, and an engaging means bringing the movable split rod element 2b into engagement with the fixed split rod element 2a in a slidable manner is interposed between both split rod elements 2a, 2b and scrapers 5, 6 are mounted on the outside surfaces of the split rod elements 2a, 2b over the total lengths of the rod elements 2a, 2b and the movable split rod element 2b is slid in the direction from a thin-walled side to a thickwalled side through a slide operation part piece 8 provided to the base end part of the movable split rod element 2b to reduce the diameter of the cleaning device main body 2.