| 摘要 |
<p>Light from an LED element provided on a surface of an LED substrate 7 provided outside of a wall surface of a heating chamber 2 passes through an illumination hole 1 that has a quadrilateral shape, and is projected in the chamber. In this case, since the LED element provided in a vicinity of the wall surface has a small light source and has high directivity of light, even when the size of the illumination hole 1 does not affect radio wave shielding properties, and the light is not hindered from passing through the quadrilateral illumination hole 1, whereby the interior of the chamber can be illuminated without decreasing the transmittance of light.</p> |
