A multilevel inverter (100, 200, 300), comprising: a plurality of direct current input terminals (P1, G, N, b1-b5) disposed in order of descending potential from a first to an n th direct current input terminal, with n being an odd number of 3 or more; first to (n - 1) th switching elements (U1, V1, W1, U4, V4, W4, X1, Y1, Z1, X2, Y2, Z2, X4, Y4, Z4) connected in series between the first direct current input terminal and n th direct current input terminal; n th to (n-1) (3/2) th switching elements (110, 310), wherein each one is a reverse blocking switching element that is connected between one of first to (n - 2) th connection points, which are connection points of pairs of the first to (n - 1) th switching elements (U1, V1, W1, U4, V4, W4, X1, Y1, Z1, X2, Y2, Z2, X4, Y4, Z4), and correspondingly one of the second to (n - 1) th direct current input terminals (G, b2-b4); alternating current output terminals (Ou, Ov, Ow) each one connected to one connection point of the pairs of first to (n - 1) th switching elements (U1, V1, W1, U4, V4, W4, X1, Y1, Z1, X2, Y2, Z2, X4, Y4, Z4); a control unit (120, 220, 320) that is configured to generate control signals for switching between a turning on and turning off of the first to (n-1) (3/2) th switching elements; characterized by a control signal interrupt circuit (140, 240, 340) that is configured to interrupt each of the control signals, after receiving an output interrupt signal, regardless of the state of the control signals, in sequence from that of the switching element of the first to (n-1) (3/2) th switching elements, which is directly connected to the direct current input terminal (P1, G, N, b1-b5) having the greatest difference in potential from a potential of the ((n + 1)/2) th direct current input terminal (G, b3), to that of the switching element of the first to (n-1) (3/2) th switching elements, which is directly connected to the direct current input terminal (PI, G, N, b1-b5) having the smallest difference in potential from a potential of the ((n + 1)/2) th direct current input terminal (G, b3), to thereby turn off the switching elements; and a monitoring unit that is configured to output a diagnostic signal to the control signal interrupt circuit (140, 240, 340), and to diagnose a breakdown of the control signal interrupt circuit (140, 240, 340) based on a response of the control signal interrupt circuit (140, 240, 340) against the diagnostic signal. a plurality of direct current input terminals (P1, G, N, b1-b5) disposed in order of descending potential from a first to an n th direct current input terminal, with n being an odd number of 3 or more; first to (n - 1) th switching elements (U1, V1, W1, U4, V4, W4, X1, Y1, Z1, X2, Y2, Z2, X4, Y4, Z4) connected in series between the first direct current input terminal and n th direct current input terminal; n th to (n-1) (3/2) th switching elements (110, 310), wherein each one is a reverse blocking switching element that is connected between one of first to (n - 2) th connection points, which are connection points of pairs of the first to (n - 1) th switching elements (U1, V1, W1, U4, V4, W4, X1, Y1, Z1, X2, Y2, Z2, X4, Y4, Z4), and correspondingly one of the second to (n - 1) th direct current input terminals (G, b2-b4); alternating current output terminals (Ou, Ov, Ow) each one connected to one connection point of the pairs of first to (n - 1) th switching elements (U1, V1, W1, U4, V4, W4, X1, Y1, Z1, X2, Y2, Z2, X4, Y4, Z4); a control unit (120, 220, 320) that is configured to generate control signals for switching between a turning on and turning off of the first to (n-1) (3/2) th switching elements; characterized by a control signal interrupt circuit (140, 240, 340) that is configured to interrupt each of the control signals, after receiving an output interrupt signal, regardless of the state of the control signals, in sequence from that of the switching element of the first to (n-1) (3/2) th switching elements, which is directly connected to the direct current input terminal (P1, G, N, b1-b5) having the greatest difference in potential from a potential of the ((n + 1)/2) th direct current input terminal (G, b3), to that of the switching element of the first to (n-1) (3/2) th switching elements, which is directly connected to the direct current input terminal (PI, G, N, b1-b5) having the smallest difference in potential from a potential of the ((n + 1)/2) th direct current input terminal (G, b3), to thereby turn off the switching elements; and a monitoring unit that is configured to output a diagnostic signal to the control signal interrupt circuit (140, 240, 340), and to diagnose a breakdown of the control signal interrupt circuit (140, 240, 340) based on a response of the control signal interrupt circuit (140, 240, 340) against the diagnostic signal.