To provide a transmitter which is used for a remote control system for vehicles etc., and can fully adjust a receivable range according to an applied condition.

The transmitter 1 transmits from an antenna 8 a radio signal (request signal of a smart entry system, for example) generated by performing ASK modulation of a carrier (rectangular wave) by a baseband signal. The transmitter has a duty control means (control circuit 4) which changes a transmitting output for the radio signal by changing the duty ratio of the carrier, as a receivable range adjustment means changing the receivable range for the radio signal.