the present invention will now be explained in connection with embodiments thereof with reference to the accompanying drawings . fig1 is an exploded perspective view showing a cartridge to be mounted on a color image forming apparatus according to the present invention and therearound . in fig1 a cartridge a has a casing 4 including therein a photosensitive drum ( image bearing member ) 1 , a cleaner 2 comprising an elastic blade slidingly contacting the drum 1 , and color ( yellow , magenta , cyan and black ) developing devices 3y , 3m , 3c and 3bk . a drive shaft 5 for the drum and drive shafts 6y , 6m , 6c and 6bk for sleeves of the developing devices 3y , 3m , 3c and 3bk are protruded from a side of the casing 4 . incidentally , in fig1 the reference symbol b denotes a driving force transmission changing unit having a drive changing means for changing the drive of the developing devices 3y , 3m , 3c and 3bk and a driving force transmitting means for transmitting a driving force from the apparatus side to the cartridge side . the unit b can easily be mounted and dismounted with respect to the cartridge a by engaging and disengaging connection pawls 7 formed on unit b with respect to connection hole members 8 formed on the cartridge a . when the unit b is mounted on the cartridge , the drum drive shaft 5 of the cartridge is fitted into a fitting hole ( not shown ) formed in an output portion of a drum pulley gear 9 disposed in the unit b , and the sleeve drive shafts 6y , 6m , 6c and 6bk are fitted into fitting holes ( not shown ) formed in output portions of drive changing clutches 16y , 16m , 16c and 16bk , respectively . the unit b mounted on the cartridge can be removably mounted on the image forming apparatus together with the cartridge . by the way , the driving force transmission changing unit b has a casing 11 including therein a relay pulley 14 , a tension pulley 15 , timing pulleys 17 , 18 having the same rotational axes as those of the drum pulley gear 9 and the relay pulley 14 , respectively , a timing belt 12 extending between the timing pulleys 17 , 18 , sleeve drive pulleys 10y , 10m , 10c and 10bk constituting input portions of the drive changing clutches 16y , 16m , 16c and 16bk , and a timing belt 13 wound around the sleeve drive pulleys 10y , 10m , 10c and 10bk , relay pulley 14 and tension pulley 15 , as well as the above - mentioned drum pulley gear 9 and the drive changing clutches 16y , 16m , 16c and 16bk . when the driving force transmission changing unit b is firstly connected to the cartridge a and then the cartridge is mounted on a body of the image forming apparatus ( not shown ), a drive transmitting portion of the drum pulley gear 9 protruded from the casing 11 is engaged by a drive transmitting gear 20 disposed at the apparatus side , with the result that the driving force is transmitted to the photosensitive drum 1 in the cartridge a and is transmitted to the timing pulley 17 , timing belt 12 , timing pulley 18 , relay pulley 14 , timing belt 13 and sleeve drive pulleys 10y , 10m , 10c and 10bk , by means of the driving force transmitting means . further , the unit b has an abutment portion 19 electrically connected to the image forming apparatus . in response to a signal from the abutment portion 19 , the operation of the drive changing clutches ( drive changing means ) 16y , 16m , 16c and 16bk is properly selected . in this way , the driving force from the apparatus side drives the photosensitive drum and the developing devices sequentially selected , thus forming the color image . now , the construction of the drive changing clutches and therearound will be briefly explained . for example , the yellow developing device 3y will be described . the drive changing clutch 16y is disposed at the back side of the sleeve drive pulley 10y in fig1 and is designed so that it can be connected to and disconnected from the sleeve drive pulley 10y by turning an electromagnet on and off to change the driving force transmitting condition in response to a signal from the apparatus side . further , the drive changing clutch 16y is provided at its output portion with the fitting hole for receiving the sleeve drive shaft 6y , so as to permit the mounting and dismounting of the driving force transmission changing unit b with respect to the cartridge and the engagement and disengagement between the fitting hole and the sleeve drive shaft 6y , as mentioned above . this arrangement is similarly adopted to other developing devices . in this way , in the illustrated embodiment , since the driving force transmission changing unit is firstly mounted to the cartridge while positioning the drive changing means thereof at hand and then the cartridge with the drive changing means is mounted on the image forming apparatus , it is not needed to perform the complicated positioning between the plurality of developing devices and the drive changing means , with the result that the positioning between the plurality of developing devices and the drive changing means can easily be effected with high accuracy . further , in the illustrated embodiment since the driving force transmission changing unit b having the driving force transmitting means and the drive changing means is formed independently from the cartridge a and can be removably mounted on the cartridge , only the cartridge may be replaced by a new one and the driving force transmitting means and the drive changing means of the driving force transmission changing unit b can be repeatedly used by the new cartridge a whenever the used - up cartridge is replaced , thus solving the problem regarding the increase in the running cost of the apparatus . incidentally , in the illustrated embodiment , while the drive of the plural developing devices were changed by the drive changing means , if it is necessary to change a driving portion ( developing devices , photosensitive drum , cleaner and the like ) in the cartridge at need , the drive changing means of the present invention can be adopted to such driving portion . next , another embodiment of the present invention will be explained with reference to fig2 . fig2 is a plan view of a cartridge and thereabout . in the cartridge , there are disposed a plurality of developing devices corresponding to yellow , magenta , cyan and black colors ; but , in fig2 only a yellow developing sleeve 3y is shown as an example . a driving force transmission changing unit b &# 39 ; according to this embodiment is generally identical to that of the previous embodiment , except that a motor m as a driving source is arranged in the driving force transmission changing unit b &# 39 ;. incidentally , the reference numeral 26y denotes a drive changing clutch similar to the above - mentioned drive changing clutch 16y , 12 &# 39 ; is a belt like in the previous embodiment . with this arrangement , since the cartridge a can be connected to the image forming apparatus only via the electrical contact , during the mounting of the cartridge , the positioning is further facilitated . further , since the photosensitive drum can be directly driven by the motor m , it is possible to avoid the uneven or non - uniform rotation of the photosensitive drum 1 which would occur in the conventional technique . incidentally , if the photosensitive drum and the developing devices are driven by the same motor , the load fluctuation in the photosensitive drum and in the developing devices will cause the subtle irregular rotation of the motor . thus , the photosensitive drum and the developing devices may be driven by different driving sources and these driving sources may be arranged in the driving force transmission changing unit . further , in the illustrated embodiments , while an example of the color cartridge was explained , in a monochromatic - color cartridge having only one developing device , the driving force transmitting means for transmitting the driving force from the apparatus side to the cartridge side may be removable with respect to both the image forming apparatus and the cartridge . in this case , an apparatus that the same advantage as the present invention is obtained . in addition , in the illustrated embodiments , while the photosensitive drum was used as the image bearing member , other photosensitive members such as a photosensitive belt may be used . while various embodiments were explained hereinabove , the present invention is not limited to such embodiment , and various alterations and modifications can be effected within the scope of the present invention .