High intensity Cu Kα X-ray was generated in helium at atmospheric (760 Torr) using a commercial millijoule high-repetition rate Ti: sapphire laser. The characteristic Kα X-ray was generated by focusing the 0.06-1.46 mJ, 100 fs and 1 kHz repetition femtosecond laser onto a solid Cu target to a spot with a 5 μm diameter. We obtained the characteristic Kα X-ray of 5.4 × 109 photos per second into 2π sr at a 1 kHz repetition rate with 5.0 × 10-6 conversion efficiency. The X-ray intensity and conversion efficiency in helium achieved the almost the same level as in vacuum. Such vacuum-free femtosecond X-ray source with a table-top laser can be a promising and easy accessible tool for time-resolved X-ray diffraction and other radiographic applications.