A work tool configured to perform an operation on a workpiece by driving a tool accessory, the work tool comprising a spindle supported to be rotatable around a driving axis and having a first clamp part on its lower end portion, the driving axis defining an up-down direction of the work tool, a clamp shaft having a shaft part and a second clamp part, the shaft part being configured to be coaxially inserted into the spindle, the second clamp part being provided on a lower end portion of the shaft part and configured to clamp the tool accessory in cooperation with the first clamp part, a holding member having a pass-through part, an engagement member configured to be rotatable around the driving axis relative to the holding member between a first position and a second position, the engagement member in the first position being allowed to pass through the pass-through part, and the engagement member in the second position being not allowed to pass through the pass-through part and being engaged with the holding member, and a first biasing member configured to bias the holding member, wherein the engagement member is configured to allow the clamp shaft to move in the up-down direction relative to the holding member when located in the first position, and to prevent the clamp shaft from moving downward relative to the holding member when located in the second position, the holding member is configured to fixedly hold the clamp shaft relative to the spindle while being biased upward by the first biasing member, with the engagement member in the second position, the holding member is configured to move relative to the spindle between a holding position and a releasing position, the holding member in the holding position fixedly holding the clamp shaft relative to the spindle, and the holding member in the releasing position allowing removal of the clamp shaft from the spindle, the holding member is configured to be held by a biasing force of the first biasing member when located in either the holding position or the releasing position, and the holding member is configured to move toward the holding position while rotating around the driving axis, when the shaft part is inserted into the spindle with the holding member in the releasing position and the engagement member in the first position, thereby causing the engagement member to relatively move to the second position, characterized in that the spindle has an inclined groove in its outer periphery, the inclined groove being inclined relative to the driving axis, the holding member has a protruding part disposed within the inclined groove, and the first biasing member has a function as a torsion spring and is configured to bias and rotate the holding member around the driving axis to thereby engage the protruding part with the inclined groove and hold the holding member in the holding position. a spindle supported to be rotatable around a driving axis and having a first clamp part on its lower end portion, the driving axis defining an up-down direction of the work tool, a clamp shaft having a shaft part and a second clamp part, the shaft part being configured to be coaxially inserted into the spindle, the second clamp part being provided on a lower end portion of the shaft part and configured to clamp the tool accessory in cooperation with the first clamp part, a holding member having a pass-through part, an engagement member configured to be rotatable around the driving axis relative to the holding member between a first position and a second position, the engagement member in the first position being allowed to pass through the pass-through part, and the engagement member in the second position being not allowed to pass through the pass-through part and being engaged with the holding member, and a first biasing member configured to bias the holding member, wherein the engagement member is configured to allow the clamp shaft to move in the up-down direction relative to the holding member when located in the first position, and to prevent the clamp shaft from moving downward relative to the holding member when located in the second position, the holding member is configured to fixedly hold the clamp shaft relative to the spindle while being biased upward by the first biasing member, with the engagement member in the second position, the holding member is configured to move relative to the spindle between a holding position and a releasing position, the holding member in the holding position fixedly holding the clamp shaft relative to the spindle, and the holding member in the releasing position allowing removal of the clamp shaft from the spindle, the holding member is configured to be held by a biasing force of the first biasing member when located in either the holding position or the releasing position, and the holding member is configured to move toward the holding position while rotating around the driving axis, when the shaft part is inserted into the spindle with the holding member in the releasing position and the engagement member in the first position, thereby causing the engagement member to relatively move to the second position, characterized in that the spindle has an inclined groove in its outer periphery, the inclined groove being inclined relative to the driving axis, the holding member has a protruding part disposed within the inclined groove, and the first biasing member has a function as a torsion spring and is configured to bias and rotate the holding member around the driving axis to thereby engage the protruding part with the inclined groove and hold the holding member in the holding position.