  We conduct 24.4~fps optical observations of repeating Fast Radio Burst (FRB)
20190520B using Tomo-e Gozen, a high-speed CMOS camera mounted on the Kiso
105-cm Schmidt telescope, simultaneously with radio observations carried out
using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We
succeeded in the simultaneous optical observations of 11 radio bursts that FAST
detected. However, no corresponding optical emission was found. The optical
fluence limits as deep as 0.068 Jy ms are obtained for the individual bursts
(0.029 Jy ms on the stacked data) corrected for the dust extinction in the
Milky Way. The fluence limit is deeper than those obtained in the previous
simultaneous observations for an optical emission with a duration $\gtrsim 0.1$
ms. Although the current limits on radio--optical spectral energy distribution
(SED) of FRBs are not constraining, we show that SED models based on observed
SEDs of radio variable objects such as optically detected pulsars, and a part
of parameter spaces of theoretical models in which FRB optical emission is
produced by inverse-Compton scattering in a pulsar magnetosphere or a strike of
a magnetar blastwave into a hot wind bubble, can be ruled out once a similar
fluence limit as in our observation is obtained for a bright FRB with a radio
fluence $\gtrsim 5$ Jy ms.
