A driver comprising: a nose portion provided in a housing and extending in a longitudinal direction, the nose portion being configured to allow a fastener to pass therethrough; a plunger configured to move in an impact direction parallel to the longitudinal direction to impact the fastener through the nose portion; a weight ; and a resilient member configured to be compressed by a motor in the longitudinal direction, a release of the compression in the resilient member causing the plunger to move in the impact direction, while causing the weight to move in a counter-impact direction which is away from the plunger , and a drive mechanism configured to cause the motor to compress the resilient member in the longitudinal direction, the drive mechanism including a first gear and a second gear meshingly engaged with the first gear , the first gear and the second gear being configured to be rotated by the motor , each of the first gear and the second gear being provided with a plurality of roller-cams arranged in a circumferential direction at predetermined intervals, characterised in that the resilient member is provided between the plunger and the weight , the resilient member having one end portion and another end portion in the longitudinal direction, the one end portion being configured to urge the plunger , and the another end portion being configured to urge the weight , wherein rotation of the first gear and the second gear causes the plurality of roller-cams of the first gear to be in abutment with one of the plunger and the weight , while causing the plurality of roller-cams of the second gear to be in abutment with an other of the plunger and the weight , thereby compressing the resilient member in the longitudinal direction. a nose portion provided in a housing and extending in a longitudinal direction, the nose portion being configured to allow a fastener to pass therethrough; a plunger configured to move in an impact direction parallel to the longitudinal direction to impact the fastener through the nose portion; a weight ; and a resilient member configured to be compressed by a motor in the longitudinal direction, a release of the compression in the resilient member causing the plunger to move in the impact direction, while causing the weight to move in a counter-impact direction which is away from the plunger , and a drive mechanism configured to cause the motor to compress the resilient member in the longitudinal direction, the drive mechanism including a first gear and a second gear meshingly engaged with the first gear , the first gear and the second gear being configured to be rotated by the motor , each of the first gear and the second gear being provided with a plurality of roller-cams arranged in a circumferential direction at predetermined intervals, characterised in that the resilient member is provided between the plunger and the weight , the resilient member having one end portion and another end portion in the longitudinal direction, the one end portion being configured to urge the plunger , and the another end portion being configured to urge the weight , wherein rotation of the first gear and the second gear causes the plurality of roller-cams of the first gear to be in abutment with one of the plunger and the weight , while causing the plurality of roller-cams of the second gear to be in abutment with an other of the plunger and the weight , thereby compressing the resilient member in the longitudinal direction. <EOS>