A compact and highly reliable nonreciprocal circuit device can be manufactured at low cost. Marking is clearly performed on a surface of the nonreciprocal circuit device. In a method of manufacturing the nonreciprocal circuit device, after components constituting the device are joined together, solder is applied at portions where the components are bonded with each other. The magnetic force of a permanent magnet is adjusted and then laser marking is performed on a surface of a metal case. Next, the nonreciprocal circuit device is heated to perform together solder bonding, thermal aging of the permanent magnet, and the removal of stains left due to marking. Then, after checking the characteristics of the device, delivery inspection is conducted to complete the manufacturing process.