To provide a magnetic spring device with a lock mechanism capable of obtaining constant spring force even if stroke of a movable member is changed.

A magnetic spring mechanism 13 and the lock mechanism 14 are stored in a main body case 11. The magnetic spring mechanism 13 is composed of a magnet 15 provided on an inner peripheral face of the main body case 11 and a magnet 16 provided on an outer peripheral face of a movable shaft 12. The magnet 15 and the magnet 16 are opposingly arranged to make magnetic poles different. The lock mechanism 14 is composed of a plurality of steel balls 26 arranged on the outer peripheral face of the movable shaft 12 and a tapered face 25 which nips and holds the steel balls 26 between the outer peripheral face of the movable shaft 12 and it and whose diameter is contracted along the direction of sinking operation of the movable shaft 12. In this lock mechanism 14, the movable shaft 12 is locked due to pressure-contact of the steel balls 26 between the tapered face 25 and the outer peripheral face of the movable shaft 12.