A glue application unit built in a suitable for being binding machine and for being arranged under a path of a clamp unit of the binding machine so as to apply glue on back margins (s) located at both sides of a back face (r) of a book block as well as the back face (r) while the clamp unit passes through the glue application unit, both the back face (r) and the back margins (s) protruding downwardly from the clamp unit, the glue application unit comprising: a frame; a glue tank attached to the frame and filled with glue; a glue application roller arranged in the glue tank and attached to the frame for rotation about a shaft thereof extending across the path of the clamp unit, the glue application roller suitable for applying the glue to the back face (r) of the book block; a motor attached to the frame and suitable for rotating the glue application roller, a part of the glue application roller being soaked in the glue of the glue tank, the glue application roller suitable for engaging with the back face (r) of the book block at its top face covered with the glue; side glue application members attached to the frame and arranged at both sides of a path of a portion of the book block protruding downwardly from the clamp so as to engage with the back margins (s) of the book block, the side glue application members having a pair of scrapers, each of the scrapers being composed of an elastic rod-like or elongated plate-like body and a scraping portion provided at a leading end of the body, 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 said path in such a way that the scrapers contact each other in an inverted V shaped configuration to close off said path, tail ends of the bodies of the scrapers being attached to the frame or the glue tank outside said path, the scraping portions of the scrapers being positioned at the downstream of the top face of the glue application roller, whereby the scraping portions can engage with the back margins (s) of the book block by the elastic biasing of the bodies while the downwardly protruding portion of the book block passes between the scrapers. a frame; a glue tank attached to the frame and filled with glue; a glue application roller arranged in the glue tank and attached to the frame for rotation about a shaft thereof extending across the path of the clamp unit, the glue application roller suitable for applying the glue to the back face (r) of the book block; a motor attached to the frame and suitable for rotating the glue application roller, a part of the glue application roller being soaked in the glue of the glue tank, the glue application roller suitable for engaging with the back face (r) of the book block at its top face covered with the glue; side glue application members attached to the frame and arranged at both sides of a path of a portion of the book block protruding downwardly from the clamp so as to engage with the back margins (s) of the book block, the side glue application members having a pair of scrapers, each of the scrapers being composed of an elastic rod-like or elongated plate-like body and a scraping portion provided at a leading end of the body, 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 said path in such a way that the scrapers contact each other in an inverted V shaped configuration to close off said path, tail ends of the bodies of the scrapers being attached to the frame or the glue tank outside said path, the scraping portions of the scrapers being positioned at the downstream of the top face of the glue application roller, whereby the scraping portions can engage with the back margins (s) of the book block by the elastic biasing of the bodies while the downwardly protruding portion of the book block passes between the scrapers.