An ion-exchanger includes a case member provided with a cooling liquid flow-in pipe through which cooling liquid is introduced and a cooling liquid discharge pipe through which the cooling liquid is discharged, a cartridge member to be detachably accommodated in the case member, and a number of ion-exchange resin particles sealed within the cartridge member. The cartridge member is provided with an engaging portion detachably engaging with an end portion of the case member, and the case member is provided with an engagement portion to be engaged with the engaging portion provided for the cartridge member.