Provided is a novel bonding agent. A bonding agent that has an average degree of saponification of 85.0–89.0 mol% as measured in accordance with JIS K6726 and is formed from a polyvinyl alcohol polymer that satisfies condition (A). Condition (A): When the polyvinyl alcohol polymer is assessed under the following measurement conditions by liquid chromatography that uses a charged particle detector as a detector and a Thermo Scientific AcclaimTM 300 column (catalog number: 060266； carbon content: 8%； maximum pressure: 4,500 psi； particle size: 3 µm； pore diameter: 300 Å； solid phase: C18； surface area: 100 m2/g； length: 150 mm； diameter: 4.6 mm； pH: 2.5–7.5； material: Glass Lined Tubing), the value represented by expression (3) as calculated on the basis of expression (1) and expression (2) is at least 22, Pi (pA) being the detection intensity at retention time Ti (min) for all of the data obtained for the relationship between retention time and detection intensity after baseline correction for retention times from 5.0 min to 12.0 min at a data sampling period of 500 millisec. [Measurement conditions] Concentration of aqueous solution of polyvinyl alcohol polymer: 0.1 mass%； injected volume of aqueous solution of polyvinyl alcohol polymer: 2 µL； column temperature: 50̊C； flow rate: 1.0 mL/min； eluant: mixed solvent of water and methanol； gradient conditions for eluant: for measurement times from 0 min to 10 min, the ratio of water and methanol in the eluant is varied at a constant rate from 95:5 to 15:85, and for measurement times from 10 min to 15 min, the ratio of water and methanol in the eluant is constant at 15:85. Expression (1): Tn=Σ(Ti×Pi)/Σ(Pi). Expression (2): Tw=Σ(Ti2×Pi)/Σ(Ti×Pi). Expression (3): {(Tw/Tn)-1}×1000.L'invention concerne un liant. Ce liant possède un degré de saponification moyen compris entre 85,0% molaires et 89,0% molaires, tel que mesuré selon le standard JIS K6726, et est constitué d'un polymère d'alcool polyvinylique remplissant la condi
