New formula to describe a non-resonant background strength in binary breakup reactions is
considered on the basis of the Migdal-Watson (MW) formula. The background strength is assumed
to be generated by a direct breakup, which is an one-step transition from an initial bound state
to final continuum states. The strength of the direct breakup
is evaluated by the complex scaling method (CSM). We have found that the extended MW formula,
which is proposed in the present study, nicely reproduces the strength
of the direct breakup calculated by CSM. A relation of
parameters newly introduced in the extended MW formula and
a spatial size of the initial wave function is also discussed.