An X-ray analyzer comprising: an excitation source for exciting a sample to be analyzed to radiate a characteristic X-ray; an X-ray detector that detects the characteristic X-ray; a collimator that regulates a range of the characteristic X-ray incident to the X-ray detector; at least one window that is provided between the sample and the X-ray detector and allows the characteristic X-ray to pass through; and a cooling unit that cools the window to a temperature that is lower than an atmospheric temperature, wherein the cooling unit comprises a cold head, and an outer surrounding shield surrounding said collimator, window and cooling unit wherein the window is laminated with one or more layer of an aluminum film and one or more layer of an insulating film, wherein a total thickness of the aluminum film of the at least one window is equal to or greater than 150 nm and is less than 300 nm, and wherein a size of the collimator is set, in consideration of a distance between the collimator and the X-ray detector, to satisfy that a quantity of radiant heat Q defined by the following equation, is equal to or less than 10 μW, Q = σ T 1 4 − T 2 4 S 1 × 1 1 ε 1 + S 2 S 1 1 ε 2 − 1 wherein: σ is a Stefan-Boltzman constant (= 5.67 W/(m 2.K 4)); S1 is an area of an outer surrounding shield; S2 is an area of the X-ray detector viewing the outer surrounding shield via the collimator; ε 1 is the emissivity of the outer surrounding shield; ε 2 is the emissivity of a front end of a cold head; T 1 is a temperature of the X-ray detector; and T 2 is a temperature of the outer surrounding shield. an excitation source for exciting a sample to be analyzed to radiate a characteristic X-ray; an X-ray detector that detects the characteristic X-ray; a collimator that regulates a range of the characteristic X-ray incident to the X-ray detector; at least one window that is provided between the sample and the X-ray detector and allows the characteristic X-ray to pass through; and a cooling unit that cools the window to a temperature that is lower than an atmospheric temperature, wherein the cooling unit comprises a cold head, and an outer surrounding shield surrounding said collimator, window and cooling unit wherein the window is laminated with one or more layer of an aluminum film and one or more layer of an insulating film, wherein a total thickness of the aluminum film of the at least one window is equal to or greater than 150 nm and is less than 300 nm, and wherein a size of the collimator is set, in consideration of a distance between the collimator and the X-ray detector, to satisfy that a quantity of radiant heat Q defined by the following equation, is equal to or less than 10 μW, Q = σ T 1 4 − T 2 4 S 1 × 1 1 ε 1 + S 2 S 1 1 ε 2 − 1 wherein: σ is a Stefan-Boltzman constant (= 5.67 W/(m 2.K 4)); S1 is an area of an outer surrounding shield; S2 is an area of the X-ray detector viewing the outer surrounding shield via the collimator; ε 1 is the emissivity of the outer surrounding shield; ε 2 is the emissivity of a front end of a cold head; T 1 is a temperature of the X-ray detector; and T 2 is a temperature of the outer surrounding shield. σ is a Stefan-Boltzman constant (= 5.67 W/(m 2.K 4)); S1 is an area of an outer surrounding shield; S2 is an area of the X-ray detector viewing the outer surrounding shield via the collimator; ε 1 is the emissivity of the outer surrounding shield; ε 2 is the emissivity of a front end of a cold head; T 1 is a temperature of the X-ray detector; and T 2 is a temperature of the outer surrounding shield.