A recording medium determining device comprising: a light irradiating portion that irradiates a recording medium with visible light; a regular reflection light receiving portion that receives regular reflection light regularly reflected by the recording medium irradiated with light from the light irradiating portion; and a diffused reflection light receiving portion that receives diffused reflection light diffusely reflected by the recording medium irradiated with light from the light irradiating portion, characterised by the recording medium determining device further comprising a determining portion arranged to determine the type of recording medium on the basis of: a combination of light intensities of two visible light components among three visible light components with different wavelengths to one another that are received by the regular reflection light receiving portion, and a combination of light intensities of two visible light components among three visible light components with different wavelengths to one another that are received by the diffused reflection light receiving portion, wherein at least one of the two components received by the regular reflection light receiving portion on the basis of which the determining portion determines the type of recording medium is also one of the two components received by the diffused reflection light receiving portion on the basis of which the determining portion determines the type of recording medium. a light irradiating portion that irradiates a recording medium with visible light; a regular reflection light receiving portion that receives regular reflection light regularly reflected by the recording medium irradiated with light from the light irradiating portion; and a diffused reflection light receiving portion that receives diffused reflection light diffusely reflected by the recording medium irradiated with light from the light irradiating portion, characterised by the recording medium determining device further comprising a determining portion arranged to determine the type of recording medium on the basis of: a combination of light intensities of two visible light components among three visible light components with different wavelengths to one another that are received by the regular reflection light receiving portion, and a combination of light intensities of two visible light components among three visible light components with different wavelengths to one another that are received by the diffused reflection light receiving portion, a combination of light intensities of two visible light components among three visible light components with different wavelengths to one another that are received by the regular reflection light receiving portion, and a combination of light intensities of two visible light components among three visible light components with different wavelengths to one another that are received by the diffused reflection light receiving portion, wherein at least one of the two components received by the regular reflection light receiving portion on the basis of which the determining portion determines the type of recording medium is also one of the two components received by the diffused reflection light receiving portion on the basis of which the determining portion determines the type of recording medium.