PURPOSE: To provide a plunger which is constituted to adhere and couple together a rod-form member made of ceramic on the tip side and a member made of a metal with a sleeve part on the base end side as an uniform adhesion layer is formed.

CONSTITUTION: A notch 82 extending in the axial direction of a plunger 62 throughout the whole of a base end body 78 is formed in the base end part 78 of a rod-form member 70 made of ceramic inserted in the sleeve part 76 of a member 72 made of a metal. When the inner periphery of a base end part 78 and/or a sleeve part 76 is coated with an adhesive and the base end part 78 is fitted in the sleeve part 76, air remaining in a position deep in the sleeve 76 is smoothly discharged through the notch 82 to the outside of the sleeve part 76.