A system for measuring a gas concentration, comprising: a ball sensor having: a piezoelectric ball, a sensor electrode configured to generate a collimated beam of a surface acoustic wave including a fundamental wave of a first frequency and a harmonic wave of a second frequency, which propagates through an orbital path on the piezoelectric ball, and a sensitive film deposited on the piezoelectric ball, configured to adsorb a target gas, the sensitive film is arranged in a position where the collimated beam of the surface acoustic wave passes through; and a signal processing unit having: a signal generator configured to transmit a burst signal to the sensor electrode so as to excite the collimated beam propagating around the piezoelectric ball, a signal receiver configured to receive burst signals of the collimated beam through the sensor electrode after the collimated beam has propagated a predetermined number of turns around the piezoelectric ball, and a waveform data processor configured to calculate the gas concentration of the target gas and the ball temperature by first and second relative changes in delay times of the first and second frequencies, respectively, using waveform data of the burst signals, wherein, when calculating the gas concentration and the ball temperature, the waveform data processor calculates first and second objective changes in delay times by the first and second relative changes, the first objective change due to the gas concentration, the second objective change due to the ball temperature. a ball sensor having: a piezoelectric ball, a sensor electrode configured to generate a collimated beam of a surface acoustic wave including a fundamental wave of a first frequency and a harmonic wave of a second frequency, which propagates through an orbital path on the piezoelectric ball, and a sensitive film deposited on the piezoelectric ball, configured to adsorb a target gas, the sensitive film is arranged in a position where the collimated beam of the surface acoustic wave passes through; and a piezoelectric ball, a sensor electrode configured to generate a collimated beam of a surface acoustic wave including a fundamental wave of a first frequency and a harmonic wave of a second frequency, which propagates through an orbital path on the piezoelectric ball, and a sensitive film deposited on the piezoelectric ball, configured to adsorb a target gas, the sensitive film is arranged in a position where the collimated beam of the surface acoustic wave passes through; and a signal processing unit having: a signal generator configured to transmit a burst signal to the sensor electrode so as to excite the collimated beam propagating around the piezoelectric ball, a signal receiver configured to receive burst signals of the collimated beam through the sensor electrode after the collimated beam has propagated a predetermined number of turns around the piezoelectric ball, and a waveform data processor configured to calculate the gas concentration of the target gas and the ball temperature by first and second relative changes in delay times of the first and second frequencies, respectively, using waveform data of the burst signals, a signal generator configured to transmit a burst signal to the sensor electrode so as to excite the collimated beam propagating around the piezoelectric ball, a signal receiver configured to receive burst signals of the collimated beam through the sensor electrode after the collimated beam has propagated a predetermined number of turns around the piezoelectric ball, and a waveform data processor configured to calculate the gas concentration of the target gas and the ball temperature by first and second relative changes in delay times of the first and second frequencies, respectively, using waveform data of the burst signals, wherein, when calculating the gas concentration and the ball temperature, the waveform data processor calculates first and second objective changes in delay times by the first and second relative changes, the first objective change due to the gas concentration, the second objective change due to the ball temperature.