PROBLEM TO BE SOLVED: To provide an illuminator reduced in operation cost.SOLUTION: The illuminator is configured such that: a light source panel 3 functions as a shelf board and can support a cultivation bed the light source panel 3 includes a box-like housing body 10, an LED 21 mounted inside the housing body 10, and a plate-like light-guiding part 30 mounted inside the housing body 10 and dispersing the light from the LED 21 downward and into a planar state. According to the illuminator, heat from the LED 21 is transmitted to a cultivation bed via the housing body 10 and released from the cultivation bed and thereby has no need of forcibly circulating coolant water unlike a conventional one, so that operation cost is reduced.
