  In 2018, Funakoshi, Hashizume, Ito, Kobayashi, and Murai used a deformation
of spherical curves called deformation type $\alpha$. Then, it was showed that
if two spherical curves $P$ and $P'$ are equivalent under the relation
consisting of deformations of type RI and type RIII up to ambient isotopy, and
satisfy certain conditions, then $P'$ is obtained from $P$ by a finite sequence
of deformations of type $\alpha$. In this paper, we introduce a new type of
deformations of spherical curves, called deformation of type $\beta$. The main
result of this paper is: Two spherical curves $P$ and $P'$ are equivalent under
(possibly empty) deformations of type RI and a single deformation of type RIII
up to ambient isotopy if and only if reduced(P) and reduced(P') are transformed
each other by exactly one deformation which is of type RIII, type $\alpha$, or
type $\beta$ up to ambient isotopy, where reduced(Q) is the spherical curve
which does not contain a $1$-gon obtained from a spherical curve $Q$ by
applying deformations of type RI up to ambient isotopy.
