The main object of the present invention is to provide 2- {4- [N- (5,6-diphenylpyrazin-2-yl) -N-isopropylamino] butyloxy} -N- (methylsulfonyl) acetamide (hereinafter “Compound A”). To provide new crystals. In the powder X-ray diffraction spectrum, a type I crystal of compound A showing diffraction peaks at least at the following diffraction angles 2θ: 9.4 degrees, 9.8 degrees, 17.2 degrees, and 19.4 degrees. A type II crystal of Compound A which exhibits diffraction peaks at least in the following diffraction angles 2θ: 9.0 degrees, 12.9 degrees, 20.7 degrees and 22.6 degrees in a powder X-ray diffraction spectrum. Compound A type III crystal showing diffraction peaks at least in the following diffraction angles 2θ: 9.3 degrees, 9.7 degrees, 16.8 degrees, 20.6 degrees, and 23.5 degrees in the powder X-ray diffraction spectrum .本発明の主目的は、２－｛４－［Ｎ－（５，６－ジフェニルピラジン－２－イル）－Ｎ－イソプロピルアミノ］ブチルオキシ｝－Ｎ－（メチルスルホニル）アセトアミド（以下、「化合物Ａ」という。）の新規な結晶を提供することにある。粉末Ｘ線回折スペクトルにおいて、少なくとも次の回折角２θ：９．４度、９．８度、１７．２度及び１９．４度に回折ピークを示す、化合物ＡのＩ型結晶。粉末Ｘ線回折スペクトルにおいて、少なくとも次の回折角２θ：９．０度、１２．９度、２０．７度及び２２．６度に回折ピークを示す、化合物ＡのＩＩ型結晶。粉末Ｘ線回折スペクトルにおいて、少なくとも次の回折角２θ：９．３度、９．７度、１６．８度、２０．６度及び２３．５度に回折ピークを示す、化合物ＡのＩＩＩ型結晶。
