An ultra-high-pressure mercury lamp according to various embodiments is an ultra-high-pressure mercury lamp in which a luminous tube employing a quartz bulb is attached to a neck part of a reflector by injecting first cement, and a metal base is attached to the neck-part end of the luminous tube by injecting second cement, wherein, if a is the outer diameter of the first cement and second cement after injection, b is the total axial depth of the first cement and second cement after injection, and c is the outer diameter of the quartz bulb in the vicinity of the luminous tube where the metal base is attached, the following relationships are satisfied: 1.3