A power conversion device comprising: a cell unit configured to supply AC power having a variable frequency to an electric motor (L); a first sensor (VM; AM; TM; 7) provided for the cell unit , the first sensor (VM; AM; TM; 7) being configured to measure a value relating to a first monitoring item of the cell unit ; a second sensor (VM; AM; TM; 7) provided for the cell unit , the second sensor (VM; AM; TM; 7) being configured to measure a value relating to a second monitoring item of the cell unit ; a storage ; a first controller configured to monitor an output result of the first sensor (VM; AM; TM; 7) and an output result of the second sensor (VM; AM; TM; 7) in both a first state in which a sign of a malfunction has not occurred in the power conversion device and a second state in which the sign of the malfunction has occurred in the power conversion device , and to control or protect the cell unit on the basis of at least one of the output result of the first sensor (VM; AM; TM; 7) and the output result of the second sensor (VM; AM; TM; 7); a second controller configured to, in a case in which the cell unit is in the first state, store the output result of the first sensor (VM; AM; TM; 7) measured at each first sampling cycle in the storage over at least a first period without storing the output result of the second sensor (VM; AM; TM; 7) in the storage , and configured to, in a case in which the cell unit transitions to the second state in which a change in at least one of the output result of the first sensor (VM; AM; TM; 7) and the output result of the second sensor (VM; AM; TM; 7) satisfies a first condition, execute a third operation of storing the output result of the second sensor (VM; AM; TM; 7) in the storage instead of the output result of the first sensor (VM; AM; TM; 7), wherein the first monitoring item is different from the second monitoring item. a cell unit configured to supply AC power having a variable frequency to an electric motor (L); a first sensor (VM; AM; TM; 7) provided for the cell unit , the first sensor (VM; AM; TM; 7) being configured to measure a value relating to a first monitoring item of the cell unit ; a second sensor (VM; AM; TM; 7) provided for the cell unit , the second sensor (VM; AM; TM; 7) being configured to measure a value relating to a second monitoring item of the cell unit ; a storage ; a first controller configured to monitor an output result of the first sensor (VM; AM; TM; 7) and an output result of the second sensor (VM; AM; TM; 7) in both a first state in which a sign of a malfunction has not occurred in the power conversion device and a second state in which the sign of the malfunction has occurred in the power conversion device , and to control or protect the cell unit on the basis of at least one of the output result of the first sensor (VM; AM; TM; 7) and the output result of the second sensor (VM; AM; TM; 7); a second controller configured to, in a case in which the cell unit is in the first state, store the output result of the first sensor (VM; AM; TM; 7) measured at each first sampling cycle in the storage over at least a first period without storing the output result of the second sensor (VM; AM; TM; 7) in the storage , and configured to, in a case in which the cell unit transitions to the second state in which a change in at least one of the output result of the first sensor (VM; AM; TM; 7) and the output result of the second sensor (VM; AM; TM; 7) satisfies a first condition, execute a third operation of storing the output result of the second sensor (VM; AM; TM; 7) in the storage instead of the output result of the first sensor (VM; AM; TM; 7), wherein the first monitoring item is different from the second monitoring item. <EOS>