The present invention aims to provide a crystalline polyester resin which satisfies both of a high melting point and a high fluidity, and a flame-retardant sealing resin composition using the same. A crystalline polyester resin (A) containing polycarboxylic acid components and polyhydric alcohol components as copolymerizing components, characterized in that a copolymerizing rate of a 2,6-naphthalenedicarboxylic acid component is from 40 to 100 molar % when a total of the polycarboxylic acid components in the crystalline polyester resin (A) is taken as 100 molar %, that a 1,4-butanediol component is copolymerized as a polyhydric alcohol component, and that a copolymerizing rate of the 1,4-butanediol component is 40 molar % or less when a total of the polyhydric alcohol components is taken as 100 molar %.

The present invention aims to provide a crystalline polyester resin which satisfies both of a high melting point and a high fluidity, and a flame-retardant sealing resin composition using the same. A crystalline polyester resin (A) containing polycarboxylic acid components and polyhydric alcohol components as copolymerizing components, characterized in that a copolymerizing rate of a 2,6-naphthalenedicarboxylic acid component is from 40 to 100 molar % when a total of the polycarboxylic acid components in the crystalline polyester resin (A) is taken as 100 molar %, that a 1,4-butanediol component is copolymerized as a polyhydric alcohol component, and that a copolymerizing rate of the 1,4-butanediol component is 40 molar % or less when a total of the polyhydric alcohol components is taken as 100 molar %.