A compound represented by the following Formula (1) that is effective for the treatment of Paget's disease of bone or hypercalcemia or a medically acceptable solvate thereof;
[wherein R
1
refers to hydrogen atom, C
1
-C
6
alkyl group optionally substituted with hydrogen group or C
1
-C
6
alkoxy group optionally substituted with hydroxyl group, R
2a
and R
2b
refer to hydrogen atom, C
1
-C
10
alkyl group optionally substituted with hydroxyl group, C
6
-C
10
aryl group optionally substituted with hydroxyl group or C
7
-C
12
aralkyl group optionally substituted with a hydroxyl group, or are combined to represent ethylene group. However, a compound in which R
1
is a hydrogen atom or a methyl group and R
2a
and R
2b
are hydrogen atoms is excluded].