A mineral material processing plant includes a frame, and a crusher and a screen which are supported on the frame, and a conveyor which is, in an operation position, arranged to discharge material which is fed into the plant to said crusher or screen. The conveyor includes separate first conveyor and second conveyor which are connectable successively to a transport connection, and the first conveyor is arranged to be moved to a transport position mainly to a first side of the crusher, and the second conveyor is fixed above the screen to be moved with the screen to the transport position mainly to a second side of the crusher. A method for operating a processing plant is also disclosed.