A plant sensor includes a light source section having first and second light emitters configured to irradiate the first and second measuring light toward the object to be measured, respectively, and a light receiver configured to receive reflected light from the object to be measured , and output light-receiving signals, a controller configured to control emission of the first and second light emitters at a different timing, an integrator configured to integrate the light-receiving signals, and output an integration signal, and a calculator configured to calculate, according to the integration signal, a reflection rate as a ratio of light volume of the reflected light of the first measuring light from the object to be measured to light volume of the first measuring light, a reflection rate as a ratio of light volume of the reflected light of the second measuring light from the object to be measured to light volume of the second measuring light, and obtains information regarding a growing condition of the object to be measured.
