The first external electrode has a main body portion a part of which is buried in a side wall of a case and joining portions protruding from an end of the main body portion toward the inside of the case. Each joining portion of the first external electrode is formed to have a thickness smaller than that of the main body portion, and an end portion of each joining portion is directly joined onto a wiring pattern of the insulating substrate through ultrasonic joining. Therefore, a load and ultrasonic vibration necessary for joining the joining portion onto the wiring pattern can be suppressed, which makes it possible to directly join the first external electrode onto the wiring pattern of the insulating substrate without damaging an insulating member of the insulating substrate.