The present invention relates to a kind of transmission mechanism (9) to be used for needle placement (1), driving mechanism (9) includes rotatable wheel (10), and to have closed geometric shape with recess (12) include bending section (12.1) and linear portion (12.2), whereinAt least one crossbeam (15,16) movably and it is engageable to injection needle (2) in retracted position (RP) and extended position (EP), the crossbeam (15,6) includes cam (15.1, (10) 0 it is adapted to engage with recess (10) 1.
