The MR-J4-350TM4-ECT is a Mitsubishi servo amplifier from the MR-J4 series, delivering 3.5 kW rated output from a 3-phase 400 VAC supply.
The 3.5 kW output rating matches a servo motor of that mechanical power class on a 400 VAC three-phase line. The EtherCAT interface locks the amplifier into a specific fieldbus architecture — if your controller speaks EtherCAT, this is a plug-and-play choice; if not, you'd need a different interface variant from the MR-J4 family.