PURPOSE: To smoothly subject a sealing frame and a cap to seam joining by forming tapered rollers provided in the directions to separate mutually on the lower ends of a couple of electrode holding arms into a shape to reduce the diameter of the electrode holding arms.

CONSTITUTION: The micro parallel seam joining device where the cap 6 is mounted on a vessel main body 1 to store a semiconductor device and while a couple of tapered roller electrodes 32 are rolled around the cap 6, energizing is carried out between both electrodes is provided with the couple of electrode holding arms 30 capable of relatively moving along the periphery of the cap 6 and the freely rotatable tapered roller electrodes 32 provided projectingly in the directions to separate mutually on the lower ends of these electrode holding arms 30 and having the reduced diameter on the electrode holding arm 30 sides. Consequently, when obstacles such as pins 10 are projected on the outside of the sealing frame, the cap can be subjected to seam joining to the sealing frame without interfering with these obstacles.