I'm pretty sure it's just 120V (or whatever the US voltage is), but I'll check.  I'm wondering if there's anything special about the way an espresso maker works that would mean it wouldn't work well with the use of a transformer.  We have some big-mama transformers, so I know we have some that are large enough. . .but some things just don't work well because of the electrical wavelength (is that the right term?)
 -- for example U.S. Voltage clocks won't keep time properly and electric dog clippers become horrifically loud.

 

Let me check on the voltage, though. . .I doubt it's dual-voltage because aside from Macs very few things are manufactured to handle both 120 & 240.