The Fuji FRN3.7E1S-4C is a FRENIC Series high-performance inverter sized for a 3.7 kW motor on a three-phase 400 V supply. This is the compact, standard-duty frame — the S enclosure is IP20, so it's meant for a clean panel, not out in the grease. If you're swapping one into a line, the 3.7 kW rating is what governs the motor match; the 400 V input tells you the bus voltage it expects.
The 3.7 kW rating is the nominal applied motor power — that's the size of standard 4-pole induction motor this drive is built to run. The three-phase 400 V input covers 380-480 VAC grids common in industrial plants. The high-performance/compact designation (E in the code) means it's got the processing for demanding torque control, not just a basic V/Hz pump drive.