The glue application unit comprises side glue application members which have a pair of scrapers (7, 7) and can engage with the back margins (s) of the book block (P). The scrapers consist of elastic rod-like bodies (7a) and scraping portions (7b) provided at leading ends of the bodies. The scrapers obliquely extending in a direction of movement of the book block from the outside of the path of the downwardly protruding portion of the book block into the path in such a way that the scrapers contact each other in an inverted V shaped configuration. The scraping portions engage with the back margins of the book block by the elastic biasing of the bodies while the downwardly protruding portion of the book block passes between the scrapers.