To provide an agrochemical spreader mounted on rice transplanter avoiding faults caused by breakage of a cable and carrying out spreading even in scattering mud without any trouble.

The agrochemical spreader mounted on rice transplanter includes a signal transmitting system 5a generating cyclic signals synchronized with the transplanting operation of the rice transplanter and converting the signals into a radio wave and transmitting to space, a receiver receiving the radio wave signal transmitted from the signal transmitting system 5a, and a spreading mechanism for spreading the agrochemical which spread the chemicals by receiving the radio signals as a trigger.