A projecting part 11A and a recessed part 12A which engage with each other are formed on a master jaw 11 and a top jaw 12. In the master jaw 11, a movable pin 20 movable in an axial direction and a shaft 30 movable in a radial direction is disposed, and the movable pin 20 is engaged with the shaft so that the movable pin 20 can be moved in the axial direction. The top jaw 12 is provided with a pin hole 12c into which the movable pin 20 can be inserted. The movable pin 20 is locked, by rotating the shaft 30 by a predetermined amount, at a first position in which the movable pin 20 is inserted in the pin hole 12c or at the second position in which the movable pin 20 is extracted from the pin hole 12c.

A projecting part 11A and a recessed part 12A which engage with each other are formed on a master jaw 11 and a top jaw 12. In the master jaw 11, a movable pin 20 movable in an axial direction and a shaft 30 movable in a radial direction is disposed, and the movable pin 20 is engaged with the shaft so that the movable pin 20 can be moved in the axial direction. The top jaw 12 is provided with a pin hole 12c into which the movable pin 20 can be inserted. The movable pin 20 is locked, by rotating the shaft 30 by a predetermined amount, at a first position in which the movable pin 20 is inserted in the pin hole 12c or at the second position in which the movable pin 20 is extracted from the pin hole 12c.

A master jaw of the chuck device includes a recessed portion recessed in a direction parallel to an axis of a spindle, and a locking portion provided outside the recessed portion in a direction orthogonal to the axis. The sub jaw includes an insertion member inserted into the recessed portion from a direction parallel to the axis by an elastic force of an elastic member, a plate located on a side opposite to the biasing member in a state of being attached to the master jaw and clamping the master jaw between the plate and the insertion member inserted into the recessed portion, and a locked portion configured to come into contact with and be locked to the locking portion from an inside in a direction orthogonal to the axis in a state in which the insertion member is inserted into the recessed portion.