Method for producing a decontaminant, wherein the method comprises: providing a plant-derived material containing silicon, carbonizing the plant-derived material at 400°C to 1400°C to obtain a porous carbon material precursor, treating the porous carbon material precursor with an acid or an alkali to obtain a porous carbon material and performing a gas activation of the porous carbon material by using oxygen, water vapor, carbon dioxide or air as an activator, and heating the porous carbon material under such an atmosphere, at 700°C to 1400°C for several tens of minutes to several hours, to obtain a decontaminant in the form of a porous carbon material, wherein (a) the porous carbon material having a value of a specific surface area based on a nitrogen BET method of 1 x 10 2 m 2 /g or more, a volume of fine pores based on a BJH method of 0.3 cm 3 /g or more, wherein as a fine pore, a "meso fine pore" having a pore diameter from 2 nm to 50 nm, a "micro fine pore" having a pore diameter smaller than 2 nm, and a "macro fine pore" having a pore diameter exceeding 50 nm are included, and a particle size of 75 μm or more, (b) the porous carbon material when dried at 120 °C and heated for 12 hours up to 800 °C in dry air results in a content of a residue on ignition (ash residue) of 15 % by mass or less, (c) the bulk density of the porous carbon material is 0.1 g/cm 3 or more and 0.8 g/cm 3 or less, and (d) the porous carbon material has at least one peak in the range of 3 nm to 20 nm, in a pore diameter distribution of a non-localized density functional theory method as specified in JISZ8831-2:2010, in which a ratio of a total of volumes of fine pores that have diameters in the range of 3 nm to 20 nm, with respect to a sum total of volumes of all fines pores, is 0.2 or more. providing a plant-derived material containing silicon, carbonizing the plant-derived material at 400°C to 1400°C to obtain a porous carbon material precursor, treating the porous carbon material precursor with an acid or an alkali to obtain a porous carbon material and performing a gas activation of the porous carbon material by using oxygen, water vapor, carbon dioxide or air as an activator, and heating the porous carbon material under such an atmosphere, at 700°C to 1400°C for several tens of minutes to several hours, to obtain a decontaminant in the form of a porous carbon material, wherein (a) the porous carbon material having a value of a specific surface area based on a nitrogen BET method of 1 x 10 2 m 2 /g or more, a volume of fine pores based on a BJH method of 0.3 cm 3 /g or more, wherein as a fine pore, a "meso fine pore" having a pore diameter from 2 nm to 50 nm, a "micro fine pore" having a pore diameter smaller than 2 nm, and a "macro fine pore" having a pore diameter exceeding 50 nm are included, and a particle size of 75 μm or more, (b) the porous carbon material when dried at 120 °C and heated for 12 hours up to 800 °C in dry air results in a content of a residue on ignition (ash residue) of 15 % by mass or less, (c) the bulk density of the porous carbon material is 0.1 g/cm 3 or more and 0.8 g/cm 3 or less, and (d) the porous carbon material has at least one peak in the range of 3 nm to 20 nm, in a pore diameter distribution of a non-localized density functional theory method as specified in JISZ8831-2:2010, in which a ratio of a total of volumes of fine pores that have diameters in the range of 3 nm to 20 nm, with respect to a sum total of volumes of all fines pores, is 0.2 or more. (a) the porous carbon material having a value of a specific surface area based on a nitrogen BET method of 1 x 10 2 m 2 /g or more, a volume of fine pores based on a BJH method of 0.3 cm 3 /g or more, wherein as a fine pore, a "meso fine pore" having a pore diameter from 2 nm to 50 nm, a "micro fine pore" having a pore diameter smaller than 2 nm, and a "macro fine pore" having a pore diameter exceeding 50 nm are included, and a particle size of 75 μm or more, (b) the porous carbon material when dried at 120 °C and heated for 12 hours up to 800 °C in dry air results in a content of a residue on ignition (ash residue) of 15 % by mass or less, (c) the bulk density of the porous carbon material is 0.1 g/cm 3 or more and 0.8 g/cm 3 or less, and (d) the porous carbon material has at least one peak in the range of 3 nm to 20 nm, in a pore diameter distribution of a non-localized density functional theory method as specified in JISZ8831-2:2010, in which a ratio of a total of volumes of fine pores that have diameters in the range of 3 nm to 20 nm, with respect to a sum total of volumes of all fines pores, is 0.2 or more.