Guide vanes are supported in a two-part or multipart housing (32, 33). Housing separation takes place radially in the region of the bearing point (25) of the vane shaft so that the separating joint (36) between the housing parts (32, 33) leads through the bearing openings (34) which are designed to hold the vane shafts. The completely round opening (34) leads to the bearing point of the vane shaft having large-area support in any position. Thus high surface pressures can be avoided.