A power tool, which actuates a tool linearly in a longitudinal direction of the tool, the power tool performs a predetermined operation to a workpiece, comprising: a drive mechanism (113, 115) which actuates the tool; a rotational shaft which actuates the drive mechanism (113, 115); a swing member; and a dynamic vibration reducer which alleviates vibration generated when the power tool is performing the predetermined operation, wherein the dynamic vibration reducer includes a weight which is linearly movable in the longitudinal direction and an elastic member (155F, 155R) which biases the weight, wherein the weight is adapted to be actuated mechanically and forcibly by a motion component with respect to the longitudinal direction of a swinging motion of the swing member in a state that the weight is biased by the elastic member (155F, 155R), wherein the power tool further comprises a rotational member which integrally rotates together with the rotational shaft, wherein the swing member is adapted to be swung by a motion component with respect to a radial direction of a rotational motion of the rotational member, wherein the power tool further comprises a support shaft which is arranged to be parallel to the rotational shaft, wherein the support shaft supports the swing member as a support point of the swinging motion of the swing member, and wherein the swing member swings along the longitudinal direction by a rotational motion of the rotational shaft, characterised in that the dynamic vibration reducer includes elastic members (155F, 155R) which are respectively disposed at a front side and a rear side of the weight with respect to the longitudinal direction and bias the weight, and in that the weight is adapted to be actuated mechanically and forcibly via the elastic members (155F, 155R) by a motion component with respect to the longitudinal direction of a swinging motion of the swing member in a state that the weight is biased by the elastic members (155F, 155R). a drive mechanism (113, 115) which actuates the tool; a rotational shaft which actuates the drive mechanism (113, 115); a swing member; and a dynamic vibration reducer which alleviates vibration generated when the power tool is performing the predetermined operation, wherein the dynamic vibration reducer includes a weight which is linearly movable in the longitudinal direction and an elastic member (155F, 155R) which biases the weight, wherein the weight is adapted to be actuated mechanically and forcibly by a motion component with respect to the longitudinal direction of a swinging motion of the swing member in a state that the weight is biased by the elastic member (155F, 155R), wherein the power tool further comprises a rotational member which integrally rotates together with the rotational shaft, wherein the swing member is adapted to be swung by a motion component with respect to a radial direction of a rotational motion of the rotational member, wherein the power tool further comprises a support shaft which is arranged to be parallel to the rotational shaft, wherein the support shaft supports the swing member as a support point of the swinging motion of the swing member, and wherein the swing member swings along the longitudinal direction by a rotational motion of the rotational shaft, characterised in that the dynamic vibration reducer includes elastic members (155F, 155R) which are respectively disposed at a front side and a rear side of the weight with respect to the longitudinal direction and bias the weight, and in that the weight is adapted to be actuated mechanically and forcibly via the elastic members (155F, 155R) by a motion component with respect to the longitudinal direction of a swinging motion of the swing member in a state that the weight is biased by the elastic members (155F, 155R).