For replacing the idler rollers 51 52 53 which are arranged in a troughed manner in the upper run of the idler roller station 5 of a belt conveyor a subframe 1 according to FIGS 1 a through 1 c is provided for lifting the web belt 7 and a changing frame 2 according to FIGS 2 a through 2 d for replacing defective or worn out idler rollers