To provide a hardening device suitable for a test of selecting hardening liquid such as oil adequate for hardening a specified work to be heated.

In the hardening device 1, a quartz tube 2 to store a test specimen S, a heating furnace 3 to heat the quartz tube 2 and a vacuum box 7 having a driving mechanism 8 to vertically move the test specimen S are mounted on a flange 4 for unitization, and a vacuum vessel 5 is separably disposed below the flange 4. A sample liquid LA to harden the baked test specimen S is stored in the vacuum vessel 5.