A cash book is the special journal which is used for recording all cash receipts and cash payment. If the cash book is maintained, there is no need for preparing a cash account in the ledger. However, the other aspects of the transactions will be recorded in the ledger. Cash book serves dual role of journal as well as ledger.
Cash book is book of original entry (journal) since transaction are recorded for the first time from the source documents. It is ledger in the sense that it is designed in the form of cash account and records cash receipts on the debit side and cash payment on the credit side.