A driver circuit device which comprises: an input-side circuit and an output-side circuit which are electrically insulated, wherein the input-side circuit comprises primary-side circuits in a plurality of driver circuits (141,142), wherein the output-side circuit comprises a driving-target external device when the driver circuit device is mounted on the driving-target external device, and the output-side circuit comprises the driving-target external device and secondary-side circuits in the driver circuits (141, 142) which are all insulated from the input-side circuit of the plurality of driver boards (102,104), the driver boards (102,104) mountable on a driving-target external device; wherein the driver circuits (141, 142) which are formed on the driver boards (102,104) are configured to apply a drive signal generated using power and a signal which are externally input to the primary-side circuits in the driver circuits (141, 142), to semiconductor elements (Q1, Q2) provided in the external device to drive the semiconductor elements (Q1, Q2), the driver boards (102, 104) comprise a lower circuit board connectable to the external device, and an upper circuit board which is disposed above the lower circuit board while a space is kept between facing circuit surfaces of the upper circuit board and the lower circuit board; wherein the upper circuit board comprises the primary-side circuit of the driver circuits (141, 142), wherein a first insulation distance is kept in the upper circuit board between the input-side circuit and the output-side circuit; characterized in that the driver circuit device further comprises: an insulating partition member disposed in the space between a circuit surface of the upper circuit board and a circuit surface of the lower circuit board to partition a gap between the circuit surfaces; and wherein the lower circuit board comprises the secondary side circuits in the driver circuits (141, 142) forming part of the output-side circuit, wherein between the circuit surfaces a second insulation distance is kept, the second insulation distance being made smaller than the first insulation distance owing to the partition member. wherein the output-side circuit comprises a driving-target external device when the driver circuit device is mounted on the driving-target external device, and the output-side circuit comprises the driving-target external device and secondary-side circuits in the driver circuits (141, 142) which are all insulated from the input-side circuit of the plurality of driver boards (102,104), the driver boards (102,104) mountable on a driving-target external device; wherein the driver circuits (141, 142) which are formed on the driver boards (102,104) are configured to apply a drive signal generated using power and a signal which are externally input to the primary-side circuits in the driver circuits (141, 142), to semiconductor elements (Q1, Q2) provided in the external device to drive the semiconductor elements (Q1, Q2), the driver boards (102, 104) comprise a lower circuit board connectable to the external device, and an upper circuit board which is disposed above the lower circuit board while a space is kept between facing circuit surfaces of the upper circuit board and the lower circuit board; wherein the upper circuit board comprises the primary-side circuit of the driver circuits (141, 142), wherein a first insulation distance is kept in the upper circuit board between the input-side circuit and the output-side circuit; characterized in that the driver circuit device further comprises: an insulating partition member disposed in the space between a circuit surface of the upper circuit board and a circuit surface of the lower circuit board to partition a gap between the circuit surfaces; and wherein the lower circuit board comprises the secondary side circuits in the driver circuits (141, 142) forming part of the output-side circuit, wherein between the circuit surfaces a second insulation distance is kept, the second insulation distance being made smaller than the first insulation distance owing to the partition member. an insulating partition member disposed in the space between a circuit surface of the upper circuit board and a circuit surface of the lower circuit board to partition a gap between the circuit surfaces; and wherein the lower circuit board comprises the secondary side circuits in the driver circuits (141, 142) forming part of the output-side circuit, wherein between the circuit surfaces a second insulation distance is kept, the second insulation distance being made smaller than the first insulation distance owing to the partition member.