Disclosed is a reaction device for producing hydrocarbons from synthesis gas, in which hydrocarbons, olefins, oxygenates, etc., are produced over a Fischer-Tropsch catalyst by using synthesis gas, so that the catalyst particles can easily be from a slurry which is discharged to the outside. That is, the present invention provides a reaction device for producing hydrocarbons from synthesis gas, in which an internal filter system for separating particles enlarged due to agglomeration phenomenon of a catalyst is installed inside the reactor, and a separating device is separately disposed outside, such that it is possible to recirculate only particles having a size appropriate for performing F-T synthesis in the slurry phase, and additionally, it is possible to effectively discharge and process a catalyst aggregated due to a combination of fine catalyst particles, the catalyst chipped off during the operation, etc., liquid hydrocarbon, resulting water, etc., in the slurry phase reactor.