PURPOSE: To provide a high frequency coupler with simple structure and high reliability while cooling safely and quickly each member such as a coaxial tube inner conductor, a coaxial tube outer conductor and a high frequency window.

CONSTITUTION: This coupler is provided with high frequency windows 24, 24 intersecting orthogonally with a space 26 between a coaxial tube inner conductor 23 and a coaxial tube outer conductor 23 in the axial direction of the coaxial tube inner conductor 22 with a gap δ while being respectively adhered with an outer circumferential face of the coaxial tube inner conductor 22 and an inner circumferential face of the coaxial tube outer conductor 23 and providing a cooling water intake 28A from which a coolant is supplied to a cooling part 28 formed to the outer circumferential face of the coaxial tube outer conductor 22 and to the gap δ formed between the high frequency windows 24, 24 to the coaxial tube outer conductor 23.