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 (63A, 63B, 63C, 64A, 64B) 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 (63A, 63B, 63C) of the first gear to be in abutment with one of the plunger and the weight, while causing the plurality of roller-cams ( 64A, 64B) 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 (63A, 63B, 63C, 64A, 64B) 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 (63A, 63B, 63C) of the first gear to be in abutment with one of the plunger and the weight, while causing the plurality of roller-cams ( 64A, 64B) 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.