Vacuum pump

A vacuum pump, comprising:

• a pump housing constituted by cast iron,
• a cooling pipe which includes an outer circumferential surface and an inner circumferential surface, is constituted by stainless steel, and passes through the pump housing, the outer circumferential surface being in close contact with the pump housing, the outer circumferential surface having a layer, alloy composition of each of the stainless steel and the cast iron being changed in the layer, a thickness of the layer being at least 0.3 mm, solid solution between the layer and the pump housing being progressed, a liquid medium flowing through the cooling pipe,
• an interior space as a pump room being provided inside the pump housing,
• a thickness of the cooling pipe being 1 mm or more and 5 mm or less, and
• a first value being 30 or more and 300 or less, the first value being obtained by dividing a capacity of the pump housing except for the interior space by a second value, and the second value being obtained by multiplying a thickness of the cooling pipe by an area in which the cooling pipe is in contact with the pump housing.