A main object of the present invention is to provide new crystals of (S)-N2-[1-(4-fluorophenyl)ethyl]-4-(1-methyl-1H-pyrazol-4-yl)-N6-(pyrazin-2-yl)pyridine-2,6-diamine maleate (hereinafter, referred to as "compound A"). A Form-I crystal of the compound A, showing diffraction peaks in its X-ray powder diffraction spectrum at least at the following angles of diffraction 2θ: 6.9 degrees, 9.4 degrees, 12.5 degrees, 15.1 degrees, 16.4 degrees, 18.3 degrees, 19.0 degrees, 24.9 degrees, 25.4 degrees, 27.3 degrees, and 27.7 degrees, wherein X-ray powder diffraction spectrum is obtained by using Cu Kα radiation (λ=1.54Å). A Form-II crystal of the compound A, showing diffraction peaks in its X-ray powder diffraction spectrum at least at the following angles of diffraction 2θ: 6.9 degrees, 9.2 degrees, 12.4 degrees, 14.8 degrees, 16.5 degrees, 18.1 degrees, 18.5 degrees, 19.8 degrees, 23.6 degrees, 24.9 degrees, and 27.7 degrees, wherein X-ray powder diffraction spectrum is obtained by using Cu Kα radiation (λ=1.54Å).
