A heat-seal apparatus having an improved structure for easily replacing a heater therein. The heat-seal apparatus includes a crimping lever, a base portion for grasping and crimping the sealed portion of a sealed substance with the crimping lever to heat and seal the sealed portion, a heater mounted to the base portion for heating and sealing the sealed portion, a slackness preventing means for preventing slackness caused by thermal expansion of the heating portion, and a means for easily removing and mounting the heating portion which achieves easy removal and mounting the heating portion by pressing back and correcting displacement of the heating portion by the slackness preventing means when the crimping lever portion is separated and held open from the base portion.