We analyze the Zeeman shift in the $(v,N)=(0,0)$→${}(1,0)$ transition frequency of $X$ Li molecules ($X$: even isotopes of group II atoms), which is of interest in metrology. The Zeeman shift in the transition frequency between stretching states is found to be less than 1 mHz with a magnetic field of 1 G. $X$ ${}^{6}$Li molecules are more advantageous than $X$ ${}^{7}$Li molecules for measuring the transition frequency without the Zeeman shift because of the smaller $g$ factor of the Li nuclear spin.