  Binary black-hole mergers up to the third observing run with the minimum
false alarm rate smaller than $10^{-5}\,{\rm yr}^{-1}$ tell us that the mass
ratio of two black holes follows $m_2/m_1=0.723$ with the chance probability of
0.00301% for $M_{chirp} > 18 M_{\odot}$ where $M_{chirp}$ ($=
(m_1m_2)^{3/5}/(m_1+m_2)^{1/5}$) is called the chirp mass of binary with masses
$m_1$ and $m_2$ ($ < m_1$). We show that the relation of $m_2/m_1=0.723$ is
consistent if the binaries consist of population III stars which are the first
stars in the universe. On the other hand, it is found for $M_{chirp} < 18
M_{\odot}$ that the mass ratio follows $m_2/m_1=0.601$ with the chance
probability of 0.117% if we ignore GW190412 with $m_2/m_1\sim 0.32$. This
suggests the different origin from that for $M_{chirp }> 18 M_{\odot}$.

General Relativity and Quantum Cosmology;High Energy Astrophysical Phenomena