A book binding apparatus for perfect book binding comprising: a conveying path; a series of processing units (B to D) arranged along the conveying path for carrying out perfect book bind processing; a clamp unit provided with a pair of clamping plates (1a and 1b) and arranged for reciprocal movement along the conveying path; a clamp unit driving mechanism reciprocating the clamp unit, the perfect book bind processing being carried out while a book block passes through the series of processing units (B to D) in succession after being nipped between the pair of clamping plates (1a, 1b); two or more of the processing units (B to D) comprising pairs of members (2b, 2c; 3c, 3d; 4a, 4b) which engage or come into contact with both sides of a back portion of the book block protruding from between the pair of clamping plates (1a, 1b), and gap adjustment means (M2 to M4) moving the pairs of members (2b, 2c; 3c, 3d; 4a, 4b) in directions toward and away from each other; a control section controlling the clamp unit and the gap adjustment means (M2 to M4); and a measuring unit for measuring a thickness of the book block, whereby, before start of the book binding processing, the thickness of the book block is measured by the measuring unit, and a gap between the pair of clamping plates (1a, 1b) and gaps between the pairs of members (2b, 2c; 3c, 3d; 4a, 4b) of the processing units (B to D) are adjusted according to the measured value of the thickness of the book block, the book binding apparatus characterized in that the control section comprises a memory for storing the measured value of a thickness of a book block, and when a thickness of a next book block is measured by the measuring unit during the perfect-binding book binding processing of a previous book block, the measured value of the thickness of the next book block is stored in the memory, and the gaps between the pairs of members (2b, 2c; 3c, 3d; 4a, 4b) of the processing units (B to D) located upstream of a predetermined position on the conveying path are adjusted based on the measured value stored in the memory when the previous book block reaches the predetermined position, and the gaps between the pairs of members (2b, 2c; 3c, 3d; 4a, 4b) of the processing units (B to D) are adjusted based on the measured value stored in the memory each time the previous book block passes through the processing units (B to D) located downstream of the predetermined position, and the gap between the pair of clamping plates (1a, 1b) is adjusted based on the measured value stored in the memory at the completion of the perfect book bind processing of the previous book block. a conveying path; a series of processing units (B to D) arranged along the conveying path for carrying out perfect book bind processing; a clamp unit provided with a pair of clamping plates (1a and 1b) and arranged for reciprocal movement along the conveying path; a clamp unit driving mechanism reciprocating the clamp unit, the perfect book bind processing being carried out while a book block passes through the series of processing units (B to D) in succession after being nipped between the pair of clamping plates (1a, 1b); two or more of the processing units (B to D) comprising pairs of members (2b, 2c; 3c, 3d; 4a, 4b) which engage or come into contact with both sides of a back portion of the book block protruding from between the pair of clamping plates (1a, 1b), and gap adjustment means (M2 to M4) moving the pairs of members (2b, 2c; 3c, 3d; 4a, 4b) in directions toward and away from each other; a control section controlling the clamp unit and the gap adjustment means (M2 to M4); and a measuring unit for measuring a thickness of the book block, whereby, before start of the book binding processing, the thickness of the book block is measured by the measuring unit, and a gap between the pair of clamping plates (1a, 1b) and gaps between the pairs of members (2b, 2c; 3c, 3d; 4a, 4b) of the processing units (B to D) are adjusted according to the measured value of the thickness of the book block, the book binding apparatus characterized in that the control section comprises a memory for storing the measured value of a thickness of a book block, and when a thickness of a next book block is measured by the measuring unit during the perfect-binding book binding processing of a previous book block, the measured value of the thickness of the next book block is stored in the memory, and the gaps between the pairs of members (2b, 2c; 3c, 3d; 4a, 4b) of the processing units (B to D) located upstream of a predetermined position on the conveying path are adjusted based on the measured value stored in the memory when the previous book block reaches the predetermined position, and the gaps between the pairs of members (2b, 2c; 3c, 3d; 4a, 4b) of the processing units (B to D) are adjusted based on the measured value stored in the memory each time the previous book block passes through the processing units (B to D) located downstream of the predetermined position, and the gap between the pair of clamping plates (1a, 1b) is adjusted based on the measured value stored in the memory at the completion of the perfect book bind processing of the previous book block.