A wireless transmitter, arranged outside of a living body and capable of performing wireless transmission utilizing magnetic coupling for an in-vivo observation apparatus inside of the living body, includes: a magnetic field generator including a plurality of plane coils inside, the plurality of plane coils being arranged such that each of coil surfaces is positioned on a same plane or arranged in a layer such that the coil surfaces are parallel to each other; a power source for supplying currents to be applied to the plurality of plane coils; a phase switch for performing operation for supplying the currents supplied from the power source to the plurality of plane coils while switching phases of the currents: and a controller for controlling sequential and repeated switching of states of the currents flowing through the plurality of plane coils at each predetermined period.