belts 14 19a so that the rotation of the upper conveyance roller 12 can be transmitted to the idle roller 12a in the case where it is not necessary to sort the recording papers 5 the recording papers 5 are conveyed through a conveyance passage formed by the gate 21a which is provided corresponding to the aforementioned second belt conveyance mechanism 19 and all the recording papers 5 are put into a bin 20a for non sorting use which is located in the uppermost portion of the sorter 10 usually the aforementioned bin 20a for non sorting use is utilized not only in the case of a non sorting operation but also in the case of a sorting operation in the case of a sorting operation the aforementioned gate member 21a is changed over so that the recording sheets 5 can be sequentially sorted into the first bin 20a to the n th bin 20 next the operation of the first belt conveyance mechanism 18 in the case of a sorting operation will be described as follows the recording paper 5 is conveyed by the aforementioned upper conveyance roller 12 and idle roller 12a and after the first recording paper 5 has been put into the first bin 20a the aforementioned changeover gate 21a.