Abstract: A fluidized bed boiler (1) has a furnace (5) limited by walls (2), a grate (3) and a roof (4). Below the grate (3) in connection with the furnace (5) is arranged a steering funnel (7) in which bed material removed from the furnace (5) is led downwards. Into the steering funnel (7), between its upper and lower edge, are arranged guide plates (14, 15, 19), which are substantially divergent from the surface of the steering funnel (7), for guiding a flow of the bed material inside the steering funnel (7). The guide plates (14, 15, 19) aim to equalize the flow of the material inside the steering funnel (7) for example by preventing the development of a core flow between an inlet (24) and outlet connection (25) of the steering funnel and at the same time to get the bed material to flow on the whole cross-sectional area of the steering funnel (7).