A heat seal bar attachment device for a bag making apparatus is used to detachably attach a heat seal bar to a heater. A rod with an attachment head is inserted through the heater. A support supports the heater. A slider is accommodated in a guide recess of the support to be slidable together with the rod, and receives one end of the rod. A biasing member is disposed between the heater and the slider to bias the slider towards a bottom surface of the guide recess. A fluid supply unit is configured to supply fluid to the guide recess and stop supplying the fluid. The fluid supply unit is configured to supply the fluid to the guide recess to slide the slider together with the rod against the biasing member.