A method is described for producing an objective substance, for example, an aldehyde such as vanillin. The objective substance is produced from a carbon source or a precursor of the objective substance by using a microorganism having an ability to produce the objective substance, wherein the microorganism has been modified to have a specific carboxylic acid reductase (CAR) gene, such as a Gordonia CAR gene, Novosphingobium CAR gene, or Coccomyxa CAR gene.