An electronic-circuit-component mounting system, comprising: a component holder support device configured to support a component holder which comprises a plurality of unit spaces (170; 292) defined according to repetition of a first rule and which holds a plurality of electronic circuit components in each of the plurality of unit spaces (170; 292), each of the unit spaces being configured as component accommodation recessed portion and/or being configured to hold a plurality of components having different rotation orientations, the electronic circuit components being arranged in the same pattern in each of the unit spaces (170; 292), this pattern being defined according to a second rule; a circuit substrate support device configured to support a circuit substrate on which an electronic circuit component is to be mounted; a component holding member configured to releasably hold the electronic circuit component; a component holding position obtainer configured to sequentially obtain a plurality of component holding positions each of which is a component holding position at which the component holding member is to hold a corresponding one of the plurality of electronic circuit components held in the plurality of unit spaces (170; 292) of the component holder supported by the component holder support device; a component mounting position obtainer configured to sequentially obtain a plurality of component mounting positions each of which is a component mounting position at which a corresponding one of the plurality of electronic circuit components is to be mounted on the circuit substrate supported by the circuit substrate support device; and a relatively moving device configured to move the component holder support device and the circuit substrate support device, and the component holding member relatively to each other based on the component holding position obtained by the component holding position obtainer and the component mounting position obtained by the component mounting position obtainer, and thereafter control the component holding member to take the electronic circuit component from the component holder supported by the component holder support device, hold the electronic circuit component, and mount the electronic circuit component onto the circuit substrate supported by the circuit substrate support device. a component holder support device configured to support a component holder which comprises a plurality of unit spaces (170; 292) defined according to repetition of a first rule and which holds a plurality of electronic circuit components in each of the plurality of unit spaces (170; 292), each of the unit spaces being configured as component accommodation recessed portion and/or being configured to hold a plurality of components having different rotation orientations, the electronic circuit components being arranged in the same pattern in each of the unit spaces (170; 292), this pattern being defined according to a second rule; a circuit substrate support device configured to support a circuit substrate on which an electronic circuit component is to be mounted; a component holding member configured to releasably hold the electronic circuit component; a component holding position obtainer configured to sequentially obtain a plurality of component holding positions each of which is a component holding position at which the component holding member is to hold a corresponding one of the plurality of electronic circuit components held in the plurality of unit spaces (170; 292) of the component holder supported by the component holder support device; a component mounting position obtainer configured to sequentially obtain a plurality of component mounting positions each of which is a component mounting position at which a corresponding one of the plurality of electronic circuit components is to be mounted on the circuit substrate supported by the circuit substrate support device; and a relatively moving device configured to move the component holder support device and the circuit substrate support device, and the component holding member relatively to each other based on the component holding position obtained by the component holding position obtainer and the component mounting position obtained by the component mounting position obtainer, and thereafter control the component holding member to take the electronic circuit component from the component holder supported by the component holder support device, hold the electronic circuit component, and mount the electronic circuit component onto the circuit substrate supported by the circuit substrate support device.