  We investigate how stable circular orbits around a main compact object appear
depending on the presence of a second one by using the Majumudar--Papapetrou
dihole spacetime, which consists of the two extremal Reissner--Nordstr\" om
black holes with different masses. While the parameter range of the separation
of the two objects is divided due to the appearance of stable circular orbits,
this division depends on its mass ratio. We show that the mass ratio range
separates into four parts, and we find three critical values as the boundaries.
