A detecting apparatus and method for detecting deformation of a fixed mold plate of an injection molding machine. The apparatus includes a mounting member and an elastic member that is received in the through hole of the mounting member and generally positioned at the center thereof. The apparatus also has a contacting member that is received in the through hole and positioned near or at the first end surface, and a sliding member that is slidably received in the through hole near or at the second end surface. A blocking member is attached to the second end surface of the mounting member. A pressure sensor is fixed between the blocking member and the contacting member.