  We revisit the constraint from the recently reported cosmic birefringence on
axion-like particles with a general decay constant. A particular attention is
paid to the naturalness of the model parameter space, which has been overlooked
in the literature. We show that the observed cosmic birefringence is naturally
explained by the electroweak axion with a string-theory inspired decay constant
$F_A\simeq 10^{16}$ GeV.
