Abstract: The present invention is intended to provide a compound useful to analyze a vitamin D compound. The present invention provides an alkyne compound represented by Formula (I): where in Formula (I), A is a linear carbon chain having an alkynyl group at an end and having a vinyl group at another end; X1 is CH or 13CH; X2 is CHY, CDY, 13CHY, 13CDY, CO, 13CO, C18O, or 13C18O; m is an integer from 1 to 4; when m is 2 or more, X2s are identical or different; Y is H, D, NH2, 15NH2, OH, 18OH, SH, OR, O(CO)R, OSO3H, OSO3Na, or a sugar substituent; when Formula (I) contains two or more Ys, Ys are identical or different; R is an alcohol protective group, an alkyl group, an alkenyl group, or an aryl group; X3 is C or 13C; and at least one selected from the group consisting of X1, X2(s), and X3 is modified with a stable isotope D, 13C, 18O, or 15N.