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 . <EOS>