A variable valve device for an engine, may include a camshaft; a movable cam device fitted over the camshaft to be slidable in an axial direction of the camshaft, and configured such that cams with at least two different cam profiles and a guide protruding portion are disposed along the axial direction of the camshaft; at least one shaft groove linearly processed to have a predetermined cross-sectional shape in an external circumferential surface of the camshaft along the axial direction thereof; a cam groove provided in an internal circumferential surface of the movable cam device to communicate with the shaft groove; and an insertion member inserted into a communication space defined by the shaft groove and the cam groove such that a rotational displacement of the camshaft is transmitted to the movable cam device.