An electronic component mounter, comprising: a suction nozzle configured to mount an electronic component to a board a movable portion configured to move in an up-down direction a holder, comprising: a cladding portion configured to engage with the movable portion and a core portion 5 comprising a detection target portion wherein the core portion is configured to accommodate the suction nozzle and to move with respect to the cladding portion when the movable portion together with the cladding portion is lowered and the electronic component is grounded to the board, thereby moving the target portion in conjunction with grounding of the electronic component to the board; and a grounding detection device, comprising: a photoelectric sensor comprising a detection region that is set horizontally adjacent to the photoelectric sensor toward the detection target portion the photoelectric sensor is fixed to the movable portion and configured to emit light out of the detection region wherein the detection target portion is configured to reflect light received from the photoelectric sensor, the photoelectric sensor further configured to receive light reflected from the detection target portion and grounding discrimination section configured to discriminate between the presence or absence of the grounding based on a received reflected light signal from the photoelectric sensor; wherein the detection target portion is not completely disposed in the detection region in an ungrounded state, the ungrounded state being a state in which the electronic component is not grounded to the board. a suction nozzle configured to mount an electronic component to a board a movable portion configured to move in an up-down direction a holder, comprising: a cladding portion configured to engage with the movable portion and a core portion 5 comprising a detection target portion wherein the core portion is configured to accommodate the suction nozzle and to move with respect to the cladding portion when the movable portion together with the cladding portion is lowered and the electronic component is grounded to the board, thereby moving the target portion in conjunction with grounding of the electronic component to the board; and a grounding detection device, comprising: a photoelectric sensor comprising a detection region that is set horizontally adjacent to the photoelectric sensor toward the detection target portion the photoelectric sensor is fixed to the movable portion and configured to emit light out of the detection region wherein the detection target portion is configured to reflect light received from the photoelectric sensor, the photoelectric sensor further configured to receive light reflected from the detection target portion and grounding discrimination section configured to discriminate between the presence or absence of the grounding based on a received reflected light signal from the photoelectric sensor; wherein the detection target portion is not completely disposed in the detection region in an ungrounded state, the ungrounded state being a state in which the electronic component is not grounded to the board. a cladding portion configured to engage with the movable portion and a core portion 5 comprising a detection target portion wherein the core portion is configured to accommodate the suction nozzle and to move with respect to the cladding portion when the movable portion together with the cladding portion is lowered and the electronic component is grounded to the board, thereby moving the target portion in conjunction with grounding of the electronic component to the board; and a grounding detection device, comprising: a photoelectric sensor comprising a detection region that is set horizontally adjacent to the photoelectric sensor toward the detection target portion the photoelectric sensor is fixed to the movable portion and configured to emit light out of the detection region wherein the detection target portion is configured to reflect light received from the photoelectric sensor, the photoelectric sensor further configured to receive light reflected from the detection target portion and grounding discrimination section configured to discriminate between the presence or absence of the grounding based on a received reflected light signal from the photoelectric sensor; wherein the detection target portion is not completely disposed in the detection region in an ungrounded state, the ungrounded state being a state in which the electronic component is not grounded to the board. a photoelectric sensor comprising a detection region that is set horizontally adjacent to the photoelectric sensor toward the detection target portion the photoelectric sensor is fixed to the movable portion and configured to emit light out of the detection region wherein the detection target portion is configured to reflect light received from the photoelectric sensor, the photoelectric sensor further configured to receive light reflected from the detection target portion and grounding discrimination section configured to discriminate between the presence or absence of the grounding based on a received reflected light signal from the photoelectric sensor; wherein the detection target portion is not completely disposed in the detection region in an ungrounded state, the ungrounded state being a state in which the electronic component is not grounded to the board.