To provide a position adjusting mechanism which can lock in the axial direction and at a certain angle and is improved so that a relative motion does not occur between two members engaged at screw threads.

A first member 12 is provided with male screw threads, and a second member 13 is provided with a hole part with female screw threads. The first member 12 is engaged with the second member 13 so that relative positions in the axial direction of two members can be adjusted and parts of the screw threads are engaged mutually within an operation scope. A lock element 14 is selectively engaged with the first member 12 in the axial direction at an arbitrary position of increment angle positions of a first number. Moreover, the lock element 14 is selectively and independently engaged with the second member 13 in the axial direction at an arbitrary position of increment angle positions of a second number so that the first and second members can be locked at an arbitrary position of increment angle positions of a third number. A size of increment of the minimum angle of the increment angle position of the third number is a function of the first and second numbers.