An inverter module suitable to be coupled to a further inverter module, the inverter module comprising: a main printed circuit board including a main board; a middle plate supporting the main PCB; a plurality of auxiliary PCBs coupled to the main PCB, wherein each auxiliary PCB has one end passing through the main PCB and exposed outwardly; and a casing for accommodating the main PCB and the auxiliary PCBs, wherein one end of at least one of the plurality of auxiliary PCBs is exposed out of the casing and is suitable to be coupled to the further inverter module adjacent to the inverter module, wherein the main PCB further includes a plurality of first connectors formed on one face of the main board, wherein each first connector has a slit passing therethrough, wherein each auxiliary PCB is inserted into the slit, wherein each of the plurality of auxiliary PCBs includes: an auxiliary board; an edge connector disposed at one side of the auxiliary board and passing through the first connector; and a third connector disposed at an opposite side of the auxiliary board, wherein a plurality of slots electrically connected to a circuit of the auxiliary board are disposed on the edge connector, wherein the third connector is configured to receive an edge connector of the further inverter module wherein the casing has a plurality of slits passing through both opposing side faces thereof, wherein one end of the at least one auxiliary PCB passes through the slits of one of the opposing side faces of the casing and protrudes out of said one of the opposing side faces of the casing. a main printed circuit board including a main board; a middle plate supporting the main PCB; a plurality of auxiliary PCBs coupled to the main PCB, wherein each auxiliary PCB has one end passing through the main PCB and exposed outwardly; and a casing for accommodating the main PCB and the auxiliary PCBs, wherein one end of at least one of the plurality of auxiliary PCBs is exposed out of the casing and is suitable to be coupled to the further inverter module adjacent to the inverter module, wherein the main PCB further includes a plurality of first connectors formed on one face of the main board, wherein each first connector has a slit passing therethrough, wherein each auxiliary PCB is inserted into the slit, wherein each of the plurality of auxiliary PCBs includes: an auxiliary board; an edge connector disposed at one side of the auxiliary board and passing through the first connector; and a third connector disposed at an opposite side of the auxiliary board, wherein a plurality of slots electrically connected to a circuit of the auxiliary board are disposed on the edge connector, wherein the third connector is configured to receive an edge connector of the further inverter module wherein the casing has a plurality of slits passing through both opposing side faces thereof, wherein one end of the at least one auxiliary PCB passes through the slits of one of the opposing side faces of the casing and protrudes out of said one of the opposing side faces of the casing. an auxiliary board; an edge connector disposed at one side of the auxiliary board and passing through the first connector; and a third connector disposed at an opposite side of the auxiliary board, wherein a plurality of slots electrically connected to a circuit of the auxiliary board are disposed on the edge connector, wherein the third connector is configured to receive an edge connector of the further inverter module wherein the casing has a plurality of slits passing through both opposing side faces thereof, wherein one end of the at least one auxiliary PCB passes through the slits of one of the opposing side faces of the casing and protrudes out of said one of the opposing side faces of the casing.