A method for producing an objective substance, wherein the objective substance is an aldehyde, the method comprising: producing the aldehyde by using a microorganism having an ability to produce the aldehyde, wherein the aldehyde is an aromatic aldehyde selected from the group consisting of vanillin, benzaldehyde, cinnamaldehyde, and combinations thereof, wherein the microorganism is a bacterium belonging to the family Enterobacteriaceae, such as a bacterium belonging to the genus Escherichia, such as Escherichia coli; or wherein the microorganism is a coryneform bacterium, such as a bacterium belonging to the genus Corynebacterium, such as Corynebacterium glutamicum; or wherein the microorganism is yeast, wherein the microorganism has been modified to have an aldehyde oxidoreductase gene, and wherein the aldehyde oxidoreductase gene encodes a protein selected from the group consisting of: (a) a protein comprising the amino acid sequence of SEQ ID NO: 18, 79, or 83; (b) a protein comprising the amino acid sequence of SEQ ID NO: 18, 79, or 83 but which includes substitution, deletion, insertion, and/or addition of 1 to 10 amino acid residues, and wherein said protein has aldehyde oxidoreductase activity to generate aromatic aldehydes such as vanillin, benzaldehyde, and cinnamaldehyde; (c) a protein comprising an amino acid sequence having an identity of 90% or higher to the amino acid sequence of SEQ ID NO: 18, 79, or 83, and wherein said protein has aldehyde oxidoreductase activity to generate aromatic aldehydes such as vanillin, benzaldehyde and cinnamaldehyde. producing the aldehyde by using a microorganism having an ability to produce the aldehyde, wherein the aldehyde is an aromatic aldehyde selected from the group consisting of vanillin, benzaldehyde, cinnamaldehyde, and combinations thereof, wherein the microorganism is a bacterium belonging to the family Enterobacteriaceae, such as a bacterium belonging to the genus Escherichia, such as Escherichia coli; or wherein the microorganism is a coryneform bacterium, such as a bacterium belonging to the genus Corynebacterium, such as Corynebacterium glutamicum; or wherein the microorganism is yeast, wherein the microorganism has been modified to have an aldehyde oxidoreductase gene, and wherein the aldehyde oxidoreductase gene encodes a protein selected from the group consisting of: (a) a protein comprising the amino acid sequence of SEQ ID NO: 18, 79, or 83; (b) a protein comprising the amino acid sequence of SEQ ID NO: 18, 79, or 83 but which includes substitution, deletion, insertion, and/or addition of 1 to 10 amino acid residues, and wherein said protein has aldehyde oxidoreductase activity to generate aromatic aldehydes such as vanillin, benzaldehyde, and cinnamaldehyde; (c) a protein comprising an amino acid sequence having an identity of 90% or higher to the amino acid sequence of SEQ ID NO: 18, 79, or 83, and wherein said protein has aldehyde oxidoreductase activity to generate aromatic aldehydes such as vanillin, benzaldehyde and cinnamaldehyde. (a) a protein comprising the amino acid sequence of SEQ ID NO: 18, 79, or 83; (b) a protein comprising the amino acid sequence of SEQ ID NO: 18, 79, or 83 but which includes substitution, deletion, insertion, and/or addition of 1 to 10 amino acid residues, and wherein said protein has aldehyde oxidoreductase activity to generate aromatic aldehydes such as vanillin, benzaldehyde, and cinnamaldehyde; (c) a protein comprising an amino acid sequence having an identity of 90% or higher to the amino acid sequence of SEQ ID NO: 18, 79, or 83, and wherein said protein has aldehyde oxidoreductase activity to generate aromatic aldehydes such as vanillin, benzaldehyde and cinnamaldehyde.