If a conveyor belt creeps sideways, belt training idlers are used to return it to a central position. Conventionally the training idlers do this by pivoting about an axis normal to the conveyor belt surface (i.e. they "slew"). The slewing of the present training idlers however is also accompanied by a sideways tilting movement to increase the realigning influence of the idler. The combined movement of the idler is enabled by spherical bearing (10) which lines frame (4), carrying idler roller (5), to base frame (9). This bearing acts as a modified universal joint, with one degree-of-freedom removed by support rollers (11) attached to a shaft through the spherical bearing along axis (12) in the direction of belt travel on each end of the shaft. When respective servo roller (3) [alternatively pairs of servo rollers (13) may be used] is contacted by a misaligned belt edge it serves to slew the frame (4) to which it is attached about axis (6) passing through the bearing. At the same time a respective roller (7) on frame (4) is driven down an angularly adjustable inclined track (8) attached to base frame (9) so that the idler is tilted as well as slewed.