A heat insulating material includes a porous sintered body formed of MgAl2O4 and having a porosity of 60% or more and less than 73%. In the heat insulating material, pores having a pore diameter of 0.8 μm or more and less than 10 μm occupy 30 vol % or more and less than 90 vol % of a total pore volume, pores having a pore diameter of 0.01 μm or more and less than 0.8 μm occupy 10 vol % or more and less than 60 vol % of the total pore volume, the thermal conductivity at 20° C. or higher and 1500° C. or lower is 0.45 W/(m·K) or less, and the compressive strength is 2 MPa or more.