The present invention provides an X-ray analysis device and a peak search method capable of realizing highly accurate peak searches without significantly increasing a processing time. Peak search processing includes: a step (S220) for acquiring a profile of a spectrum; a step (S240) for narrowing down a wavelength range where a true value of a peak wavelength (peak intensity) may be present, taking into account statistical fluctuation of a measured value; a step (S250) for measuring the intensity of the X-rays at the long wavelength end, the short wavelength end, and the intermediate wavelength in the narrowed wavelength range; a step (S255) for calculating a quadratic function passing through the respective measured values in the above-described three wavelengths; and a step (S260) for calculating the wavelength of the vertex of the calculated quadratic function as the peak wavelength.