A liquid supply apparatus (10) is provided. The liquid supply apparatus (10) has a cylinder (12), a piston (14) and a piston pushing apparatus. The cylinder (12) is provided with a head portion (20) with outlet (24). The cylinder (12) has a rear end opened. The piston (14) is inserted into the cylinder (12). The piston moves along the longitudinal direction of the cylinder (12) so as to inject liquid contained in the cylinder (12). The piston pushing apparatus (16) pushes the piston (14). The piston pushing apparatus (16) has a moving member contacting the rear portion of the piston (14), a electric motor and a movement transferring mechanism. The movement transferring mechanism converts the rotation of the motor into the linear movement of the moving member.