A sheet processing apparatus, comprising: a depositing section into which a sheet is placed; a withdrawal section to which a sheet is dispensed; a first storage unit which is installed within a storage housing, the storage housing comprising a safe which forms a lower housing and which comprises a lockable door, the first storage unit being used in at least one of depositing processing of the sheet placed into the depositing section and withdrawal processing of the sheet to be dispensed to the withdrawal section, the first storage unit storing a sheet, wherein the lockable door is in a front portion of the storage housing; a temporary storage section which temporarily stores a sheet; and an attachment section which detachably attaches a second storage unit to an outside of the storage housing, the second storage unit storing a sheet in a state of being isolated from an outside of the second storage unit and being used in at least one of the depositing processing and the withdrawal processing, wherein the attachment section is being provided in front of the lockable door of the storage housing and the sheet processing apparatus comprises a transport unit which is configured to transport a sheet among the depositing section, the withdrawal section, the temporary storage section, the first storage unit, and the second storage unit, the transport unit comprising a loop-shaped transport path as well as a first diversion path connecting the loop-shaped transport path and the depositing section, a second diversion path connecting the loop-shaped transport path and the withdrawal section, a third diversion path connecting the loop-shaped transport path and the temporary storage section, a fourth diversion path connecting the loop-shaped transport path and the storage housing, and a fifth diversion path connecting the loop-shaped transport path and the second storage unit; a control section which is configured to control the transport unit to perform at least one of the depositing processing and the withdrawal processing; and a recognition unit which is configured to recognize a sheet transported by the transport unit, wherein the transport unit is configured to transport a sheet placed into the depositing section to the recognition unit via the loop-shaped transport path and to transport a sheet recognized by the recognition unit from the loop-shaped transport path to the second storage unit via the fifth diversion path, and the transport unit, the recognition unit, the temporary storage section, and the control section are disposed within an upper housing of the sheet processing apparatus. a depositing section into which a sheet is placed; a withdrawal section to which a sheet is dispensed; a first storage unit which is installed within a storage housing, the storage housing comprising a safe which forms a lower housing and which comprises a lockable door, the first storage unit being used in at least one of depositing processing of the sheet placed into the depositing section and withdrawal processing of the sheet to be dispensed to the withdrawal section, the first storage unit storing a sheet, wherein the lockable door is in a front portion of the storage housing; a temporary storage section which temporarily stores a sheet; and an attachment section which detachably attaches a second storage unit to an outside of the storage housing, the second storage unit storing a sheet in a state of being isolated from an outside of the second storage unit and being used in at least one of the depositing processing and the withdrawal processing, wherein the attachment section is being provided in front of the lockable door of the storage housing and the sheet processing apparatus comprises a transport unit which is configured to transport a sheet among the depositing section, the withdrawal section, the temporary storage section, the first storage unit, and the second storage unit, the transport unit comprising a loop-shaped transport path as well as a first diversion path connecting the loop-shaped transport path and the depositing section, a second diversion path connecting the loop-shaped transport path and the withdrawal section, a third diversion path connecting the loop-shaped transport path and the temporary storage section, a fourth diversion path connecting the loop-shaped transport path and the storage housing, and a fifth diversion path connecting the loop-shaped transport path and the second storage unit; a control section which is configured to control the transport unit to perform at least one of the depositing processing and the withdrawal processing; and a recognition unit which is configured to recognize a sheet transported by the transport unit, wherein the transport unit is configured to transport a sheet placed into the depositing section to the recognition unit via the loop-shaped transport path and to transport a sheet recognized by the recognition unit from the loop-shaped transport path to the second storage unit via the fifth diversion path, and the transport unit, the recognition unit, the temporary storage section, and the control section are disposed within an upper housing of the sheet processing apparatus.