An ultrasonic treatment head comprising: a head body configured to be easily held by a user's hand and put on skin of a patient for treatment; and a cartridge detachably coupled to the head body and performing in-plane scanning on a treatment area by generating ultrasonic waves in accordance with operation of the head body; characterized in that the cartridge includes: a cartridge housing for keeping a transducer and liquid therein; a flat window disposed on the cartridge housing to transmit ultrasonic waves to a treatment area; a body coupler for coupling to the head body; an ultrasonic transducer generating ultrasonic waves in response to an operation signal input through the body coupler; and a fitting assembly moving the ultrasonic transducer on the flat window for in-plane scanning by a pivot motion, which is transmitted through the body coupler, of the stage, wherein the fitting assembly includes: a first support having a hole therein and coupled to the body coupler; a compression spring inserted in the hole of the first support; a second support inserted in the hole of the first support to compress the compression spring; a ball joint coupled to the second support and a transducer housing combined with the ball joint, wherein the ultrasonic transducer is fastened to the transducer housing. a head body configured to be easily held by a user's hand and put on skin of a patient for treatment; and a cartridge detachably coupled to the head body and performing in-plane scanning on a treatment area by generating ultrasonic waves in accordance with operation of the head body; characterized in that the cartridge includes: a cartridge housing for keeping a transducer and liquid therein; a flat window disposed on the cartridge housing to transmit ultrasonic waves to a treatment area; a body coupler for coupling to the head body; an ultrasonic transducer generating ultrasonic waves in response to an operation signal input through the body coupler; and a fitting assembly moving the ultrasonic transducer on the flat window for in-plane scanning by a pivot motion, which is transmitted through the body coupler, of the stage, wherein the fitting assembly includes: a first support having a hole therein and coupled to the body coupler; a compression spring inserted in the hole of the first support; a second support inserted in the hole of the first support to compress the compression spring; a ball joint coupled to the second support and a transducer housing combined with the ball joint, wherein the ultrasonic transducer is fastened to the transducer housing. a cartridge housing for keeping a transducer and liquid therein; a flat window disposed on the cartridge housing to transmit ultrasonic waves to a treatment area; a body coupler for coupling to the head body; an ultrasonic transducer generating ultrasonic waves in response to an operation signal input through the body coupler; and a fitting assembly moving the ultrasonic transducer on the flat window for in-plane scanning by a pivot motion, which is transmitted through the body coupler, of the stage, wherein the fitting assembly includes: a first support having a hole therein and coupled to the body coupler; a compression spring inserted in the hole of the first support; a second support inserted in the hole of the first support to compress the compression spring; a ball joint coupled to the second support and a transducer housing combined with the ball joint, wherein the ultrasonic transducer is fastened to the transducer housing. a first support having a hole therein and coupled to the body coupler; a compression spring inserted in the hole of the first support; a second support inserted in the hole of the first support to compress the compression spring; a ball joint coupled to the second support and a transducer housing combined with the ball joint, wherein the ultrasonic transducer is fastened to the transducer housing.