A heat treatment apparatus 1 includes a coolant passage defining body 42 to define a coolant passage 48 to supply a coolant to a workpiece 100. The coolant passage defining body 42 includes an upper member 50 and a lower member 40 as a plurality of coolant passage defining members, and is configured so that, by displacing these members 49 and 50 so as to approach each other along an up-down direction Z1 crossing a conveyance direction, the coolant passage 48 is defined in a state housing the workpiece 100. In addition, the coolant passage defining body is configured so that, by displacing the members 49 and 50 described above so as to separate from each other along the up-down direction Z1, the workpiece 100 is allowed to be let into and out of the coolant passage 48 along the conveyance direction A1.