GRID CONNECTION APPARATUS

Provided is an inverter apparatus, wherein the space necessary for installing a grid connection relay is made to be small, and the state of contacts of the grid connection relay can be monitored. When a commercial power system (30) is in normal operation state, an inverter circuit (5) is controlled to be in stopped state, and the grid connection relays (7) are controlled to be in opened state, detection of whether or not the contact of a first grid connection relay (71) or a second grid connection relay (72), which comprise the grid connection relay (7), is stuck together can be conducted before a grid connection is made between the inverter circuit (5) and the commercial power system (30), by detecting the potential difference between the W side of the first grid connection relay (71) and the Z side of the second grid connection relay (72), and the potential difference between the Y side of the first grid connection relay (71) and the X side of the second grid connection relay (72), with photocouplers (91, 95), respectively.