The present disclosure is related to an amplifier circuit in which noise components are reduced to achieve a high SN ratio, a low noise, and a small area, and an amplifier circuit IC chip. An amplifier circuit (100) includes a converter (70) configured to convert a predefined physical quantity to a resistance value, and the resistance value converted by the converter (70) is converted to a voltage value and then amplified. The converter (70) includes variable resistance sensors (71, 72) of piezoresistance elements. A bias unit (80) is configured to determine a bias current of the converter (70), and includes bias resistances (81, 82). An operation amplifier unit (90) receives, as input signals, output signals from the bias unit (80) and the converter (70), and includes feedback resistances (91, 92) respectively connected to input and output ends of a first operational amplifier (101). The first operational amplifier (101) is a whole differential operational amplifier including a common-mode feedback circuit.