  We present results obtained from ALMA CO (2-1) data of the double-barred
galaxy NGC 3504. With three times higher angular resolution (~ 0."8) than
previous studies, our observations reveal an inner molecular gas bar, a nuclear
ring, and four inner spiral arm-like structures in the central 1 kpc region.
Furthermore, the CO emission is clearly aligned with the two dust lanes in the
outer bar region, with differences in shape and intensity between them. The
total molecular gas mass in the observed region (50"x57") is estimated to be
$\sim 3.1\times 10^9 \, {\rm M}_{\odot}$, which is 17 per cent of the stellar
mass. We used the Kinemetry package to fit the velocity field and found that
circular motion strongly dominates at $R= 0.3-0.8$ kpc, but radial motion
becomes important at $R<0.3$ kpc and $R=1.0-2.5$ kpc, which is expected due to
the presence of the inner and outer bars. Finally, assuming that the gas moves
along the dust lanes in the bar rotating frame, we derived the pattern speed of
the outer bar to be $ 18\pm5$ km s$^{-1}$ kpc$^{-1}$, the average streaming
velocities on each of the two dust lanes to be 165 and 221 km s$^{-1}$, and the
total mass inflow rate along the dust lanes to be 12 M$_{\odot}$ yr$^{-1}$. Our
results give a new example of an inner gas bar within a gas-rich double-barred
galaxy and suggest that the formation of double-barred galaxies could be
associated with the existence of such gas structures.
