Abstract: The ink allows to prevent spout of the ink from the nib, and has a good penetrating and drying ability of writing to a material to be written. And the ink comprises a penetrant and a coloring agent, a humectant and water, wherein viscosity at 20° C. is from 1.2 to 10 mPa·s and surface tension is from 35 to 55 dyne/cm. The penetrant can be glycol ether represented by the following formula R1—(O—R2)x—O—R3 wherein, R1 is an alkyl group having 2 to 4 carbon atoms or a phenyl group, R2 is “—CH2—CH2—” or “—CH2CH(CH3)—”, R3 is H or an alkyl group having 1 to 6 carbon atoms, and X is an integer of 2 or 3.