The ethyl alcohol-detecting device of the present invention includes an ethyl alcohol-detecting portion that calculates an ethyl alcohol content corresponding to an ethyl alcohol concentration, based on a first subject image stored in a memory and a reference image stored in a nonvolatile memory an interfering substance-detecting portion that calculates a degree of interference corresponding to the concentration of an interfering substance, based on a second subject image stored in the memory and the reference image stored in the nonvolatile memory and a determination portion that determines that ethyl alcohol has been detected when the ethyl alcohol content is equal to or higher than a first predetermined threshold and the degree of interference is less than a second predetermined threshold, and determines that ethyl alcohol has not been detected when the ethyl alcohol content is equal to or higher than the first predetermined threshold and the degree of interference is equal to or higher than the second predetermined threshold.
