A crusher comprising: a box-like crusher frame with two end walls and two side walls connecting the end walls; at least one crusher rotor that is supported for a rotating movement inside the crusher frame against its end walls; the circumference of the crusher rotor having a plurality of crusher teeth and the crusher having counter-blade structures (6, 7) arranged to cooperate with the crusher teeth of the crusher rotor, and the material fed into the crusher for crushing being intended to be fed essentially above the centre lines of the rotor(s) and to be crushed between the crusher teeth of the crusher rotor and the counter-blade structures (6, 7); wherein two hatches (8, 9, 9') are arranged on the side of at least one side wall of the crusher, the first hatch being above the centre line of the crusher rotor and pivoted by joints at its top part to the end walls of the crusher to be turnable toward the centre line of the crusher, and the second hatch being mainly below the centre line of the crusher rotor and pivoted at its bottom part by joints to the end walls of the crusher to be turnable away from the crusher rotor, wherein the ends of the first and second hatches (8, 9) facing each other engage in the closed position, characterised in that when a hard object enters between the crusher rotor, its crusher teeth and counter-blade structure (6, 7), the crusher rotor stops and raises an alarm, wherein in cases, where the crushing does not take place against the counter-blades on the top hatch, the removal of foreign objects is started by rotating the crusher rotor in the opposite direction, in which case the foreign object comes close to the lower hatch (9, 9') that can be opened and the upper hatch is then turned inward toward the centre of the crusher, in which case the material to be crushed on top of the crusher rotor moves toward the centre of the crusher and is prevented from flowing out and next, the lower hatch (9, 9') is opened to gain clear access to the crusher rotor 4 and the foreign object can easily be removed. a box-like crusher frame with two end walls and two side walls connecting the end walls; at least one crusher rotor that is supported for a rotating movement inside the crusher frame against its end walls; the circumference of the crusher rotor having a plurality of crusher teeth and the crusher having counter-blade structures (6, 7) arranged to cooperate with the crusher teeth of the crusher rotor, and the material fed into the crusher for crushing being intended to be fed essentially above the centre lines of the rotor(s) and to be crushed between the crusher teeth of the crusher rotor and the counter-blade structures (6, 7); wherein two hatches (8, 9, 9') are arranged on the side of at least one side wall of the crusher, the first hatch being above the centre line of the crusher rotor and pivoted by joints at its top part to the end walls of the crusher to be turnable toward the centre line of the crusher, and the second hatch being mainly below the centre line of the crusher rotor and pivoted at its bottom part by joints to the end walls of the crusher to be turnable away from the crusher rotor, wherein the ends of the first and second hatches (8, 9) facing each other engage in the closed position, characterised in that when a hard object enters between the crusher rotor, its crusher teeth and counter-blade structure (6, 7), the crusher rotor stops and raises an alarm, wherein in cases, where the crushing does not take place against the counter-blades on the top hatch, the removal of foreign objects is started by rotating the crusher rotor in the opposite direction, in which case the foreign object comes close to the lower hatch (9, 9') that can be opened and the upper hatch is then turned inward toward the centre of the crusher, in which case the material to be crushed on top of the crusher rotor moves toward the centre of the crusher and is prevented from flowing out and next, the lower hatch (9, 9') is opened to gain clear access to the crusher rotor 4 and the foreign object can easily be removed.