Composite particles contained in an ink are particles of a composite of a polyester resin including a sulfonic acid group and a basic dye. The polyester resin has a glass transition point of 40° C. to 70° C. The polyester resin includes a first repeating unit derived from a polyvalent carboxylic acid having the sulfonic acid group, a second repeating unit derived from a polyvalent carboxylic acid having no sulfonic acid group, and a third repeating unit derived from a polyhydric alcohol. The content ratio of the first repeating unit relative to the total amount of the first repeating unit and the second repeating unit is at least 1.5 mol % and no greater than 20.0 mol %. The mass ratio of the polyester resin to the basic dye is at least 1.0 and no greater than 10.0.

Composite particles contained in an ink are particles of a composite of a polyester resin including a sulfonic acid group and a basic dye. The polyester resin has a glass transition point of 40 C. to 70 C. The polyester resin includes a first repeating unit derived from a polyvalent carboxylic acid having the sulfonic acid group, a second repeating unit derived from a polyvalent carboxylic acid having no sulfonic acid group, and a third repeating unit derived from a polyhydric alcohol. The content ratio of the first repeating unit relative to the total amount of the first repeating unit and the second repeating unit is at least 1.5 mol % and no greater than 20.0 mol %. The mass ratio of the polyester resin to the basic dye is at least 1.0 and no greater than 10.0.