To obtain a low-toxic calcium metabolism improver with small side effects, containing, as active ingredient, a vitamin D3 derivative.

This calcium metabolism improver contains, as active ingredient, (20S,22R)-22-methyl-1α,25-dihydroxyvitamin D3 of the formula. The compound of the formula has the binding activity on 1α,25-dihydroxyvitamin D3 receptors as high as 18 times that of 1,25-dihydroxyvitamin D3 and the affinity for vitamin D-bound protein as low as 1/500 times that of 1,25-dihydroxyvitamin D3, therefore being useful as a calcium metabolism improver such as hyperparathyroidism therapeutic agent. This improver can be administered either orally or parenterally, its dose being 0.01-5 (pref. 0.05-1)μg a day per adult in one to three portions. The compound of the formula can be prepared by photoisomerization of a (20S,22R)-22-methylprovitamin D derivative while maintaining anoxic condition followed by conducting a thermoisomerization.