To provide a tool post of a working machine for a printed circuit board which can make an axis of a tool coaxial with an axis of a collet chuck.

A sleeve 51, a holder 60 having a slit 60t formed for holding the tool at an upper end and movable in the sleeve 51, a collar 61 arranged in the sleeve 51, a first spring 53 and a second spring 62 whose spring constant is lower than the spring constant of the first spring 53 are provided. The second spring 62 is arranged between the holder 60 and the collar 61 and the first spring 53 is arranged in a lower side of the collar 61, respectively. When the tool 31 is mounted on the holder 60, during a movement of a distance m, the holder 60 urges a collet chuck by an urging force of the second spring 62. When moving a distance more than the distance m, the slit 60t is expanded by an urging force of the first spring 53.