Photocatalyst, gas sensor device and gas sensor

A gas sensor comprising:

• a gas sensor device provided with a first electrode, a second electrode, and a sensitive film that connects the first electrode to the second electrode;
• a light source that irradiates the sensitive film with light, wherein the sensitive film is made of cuprous bromide, and the cuprous bromide expresses a photocatalytic property of decomposing a substance brought into contact with the cuprous bromide by light applied from the light source;
• and
• a control unit that:
• measures a concentration of a measuring target gas based on a value detected by the gas sensor device in a case where the measuring target gas is supplied and also controls the light source,
• controls a gas supply timing and a gas supply tune for supplying the measuring target gas, and also controls a light irradiation timing and a light irradiation time for irradiating the sensitive film with light from the light source,
• controls the light source to irradiate the sensitive film with light at a timing at which the supply of the measuring target gas is stopped, and
• controls the light source to irradiate the sensitive film with light until a resistance value returns to a resistance value from the gas sensor device detected when the supply of the measuring target gas is started.