A signal decision apparatus for deciding a type of a received signal that is constituted from a plurality of subcarriers frequency division multiplexed with each other, comprising: a subcarrier separation unit operable to separate the received signal into the plurality of subcarriers, including a pilot carrier and a data carrier, characterized in that a type decision unit operable to decide, according to a relationship between the pilot carrier and the data carrier obtained as a result of the separation by the subcarrier separation unit, whether the received signal is a predetermined type of frequency-multiplexed signal including a pilot carrier that has been modulated in accordance with a first signal constellation, and a data carrier that has been modulated in accordance with a second signal constellation that is in a predetermined relationship with the first signal constellation, the type decision unit includes a phase difference information detection subunit operable to detect, according to the pilot carrier and the data carrier, phase difference information pertaining to a phase difference between the pilot carrier and the data carrier, and a decision subunit operable to decide whether the received signal is the predetermined type of frequency-multiplexed signal by deciding whether the phase difference information detected by the phase difference information detection subunit fulfils a predetermined phase difference condition that is determined based on a predetermined phase difference range that is fulfilled by a phase difference between the pilot carrier and the data carrier of the predetermined type of frequency-multiplexed signal at a time of signal reception. a subcarrier separation unit operable to separate the received signal into the plurality of subcarriers, including a pilot carrier and a data carrier, characterized in that a type decision unit operable to decide, according to a relationship between the pilot carrier and the data carrier obtained as a result of the separation by the subcarrier separation unit, whether the received signal is a predetermined type of frequency-multiplexed signal including a pilot carrier that has been modulated in accordance with a first signal constellation, and a data carrier that has been modulated in accordance with a second signal constellation that is in a predetermined relationship with the first signal constellation, the type decision unit includes a phase difference information detection subunit operable to detect, according to the pilot carrier and the data carrier, phase difference information pertaining to a phase difference between the pilot carrier and the data carrier, and a decision subunit operable to decide whether the received signal is the predetermined type of frequency-multiplexed signal by deciding whether the phase difference information detected by the phase difference information detection subunit fulfils a predetermined phase difference condition that is determined based on a predetermined phase difference range that is fulfilled by a phase difference between the pilot carrier and the data carrier of the predetermined type of frequency-multiplexed signal at a time of signal reception.