A gas concentration detection apparatus and system including a gas sensor. Voltage Vd generated across detection resistor Rd through which pump current Ip flows is differentially amplified by OP1, and offset voltage Vofs is superposed thereon to obtain a detection voltage Vout. The amplification factor applied to the differential amplification of the voltage Vd is changed by turning switch SW3 on and off. When switch SW2 is turned on, the input terminal potentials of the operational amplifier OP1 are equalized, so that voltage Vofs is output as the detection voltage Vout. The detection voltage Vout contains an error attributable to the electronic components which form the circuit. The detection voltage Vout containing the error when SW2 is turned on is acquired as a correction voltage for each amplification factor, and is used for correction at the time of detection of the concentration so as to cancel the error.