An image forming apparatus configured to allow a unit to be mounted on/demounted from and/or an external device to be connected to/disconnected from the image forming apparatus, such a unit and/or external device configured or previously configured to perform at least one of a process or a post-process on a job executed by the image forming apparatus, comprising: a connection recognition section configured to recognize that the unit is mounted and/or the external device is connected; and a control section configured to manage the unit and/or the external device and manage a job, wherein the control section is configured to receive a recognition result from the connection recognition section and check to determine whether a unit is mounted or dismounted and/or an external device is connected or disconnected, and characterised in that the control section is configured to: obtain management information for the unit and/or external device to determine if the unit and/or external device is retained and managed by a user or is mounted on or connected to another image forming apparatus that is used by the user, such units and external devices determined to be managed units and/or devices; prohibit job creation if it is determined that the job requires a unit and/or external device which is not a managed unit and/or device; allow job creation if it is determined that the job requires a managed unit and/or device, wherein when it is determined that said managed unit and/or device is not mounted and/or connected to the image forming apparatus, the job is created as a currently inexecutable job that is unable to be executed under the current apparatus configuration but which is executable when the managed unit and/or device is mounted/connected to the image forming apparatus, and execute a job when the managed unit and/or external device that is to be used for the job is mounted or connected to the image forming apparatus. a connection recognition section configured to recognize that the unit is mounted and/or the external device is connected; and a control section configured to manage the unit and/or the external device and manage a job, wherein the control section is configured to receive a recognition result from the connection recognition section and check to determine whether a unit is mounted or dismounted and/or an external device is connected or disconnected, and characterised in that the control section is configured to: obtain management information for the unit and/or external device to determine if the unit and/or external device is retained and managed by a user or is mounted on or connected to another image forming apparatus that is used by the user, such units and external devices determined to be managed units and/or devices; prohibit job creation if it is determined that the job requires a unit and/or external device which is not a managed unit and/or device; allow job creation if it is determined that the job requires a managed unit and/or device, wherein when it is determined that said managed unit and/or device is not mounted and/or connected to the image forming apparatus, the job is created as a currently inexecutable job that is unable to be executed under the current apparatus configuration but which is executable when the managed unit and/or device is mounted/connected to the image forming apparatus, and execute a job when the managed unit and/or external device that is to be used for the job is mounted or connected to the image forming apparatus. obtain management information for the unit and/or external device to determine if the unit and/or external device is retained and managed by a user or is mounted on or connected to another image forming apparatus that is used by the user, such units and external devices determined to be managed units and/or devices; prohibit job creation if it is determined that the job requires a unit and/or external device which is not a managed unit and/or device; allow job creation if it is determined that the job requires a managed unit and/or device, wherein when it is determined that said managed unit and/or device is not mounted and/or connected to the image forming apparatus, the job is created as a currently inexecutable job that is unable to be executed under the current apparatus configuration but which is executable when the managed unit and/or device is mounted/connected to the image forming apparatus, and execute a job when the managed unit and/or external device that is to be used for the job is mounted or connected to the image forming apparatus.