Image forming apparatus and image forming method

An image forming apparatus,. comprising:

• an image bearer;
• a charger configured to charge a surface of the image bearer;
• an irradiator configured to write an electrostatic latent image on the charged surface of the image bearer;
• a developing device containing a toner, the developing device configured to visualize the electrostatic latent image formed on the surface of the image bearer with the toner to form a toner image;
• a transfer device configured to transfer the toner image from the surface of the image bearer onto a transfer medium, wherein the image bearer has a Martens hardness of from 185 to 250 N/mm2, wherein the toner satisfies a relation 0.13≤X/Dn≤0.16, where X represents an average value of an amount of deformation of the toner by micro-indentation when a load reaches 3.00×10−4 N at a loading rate of 3.0×10−5N/sec under an environment of 32 degrees C. and 40%RH, and Dn represents a number average particle diameter of the toner,
• wherein the toner contains an external additive comprising:
• silica particles;
• and
• particles composed mainly of strontium titanate, the particles composed mainly of strontium titanate further containing a third element M selected from the group consisting of La, Mg, Ca, Sn, and Si.