A thermal gas sensor comprising: a substrate with a cavity portion (5; 47, 48); a thin-film support formed of stacked insulating layers (8a, 8b) is formed to lie over the cavity portion (5; 47, 48); characterized in further comprising: a first heating member and a second heating member both sandwiched between the insulating layers (8a, 8b) in the thin-film support; and a driving circuit as heating temperature control means configured to control the temperature of the first and second heating members (3,4) by supplying heating current; wherein the second heating member is located around a periphery of the first heating member, the heating temperature control means are adapted to control a temperature of the first heating member to be higher than a temperature of the second heating member, the heating temperature T2 of the second heating member is configured to be set such that T1• X4/X3+T3<T2<T1, wherein the heating temperature of the first heating member is denoted by T1, the heating temperature of the second heating member is denoted by T2, a gas temperature around the thermal gas sensor is denoted by T3, a distance from an end of the cavity portion to the first heating member is denoted by X3, and a distance from an end of the cavity portion to a center of the second heating member is denoted by X4; and the thermal gas sensor is adapted to measure a concentration of an ambient gas based on electric power applied to the first heating member. a substrate with a cavity portion (5; 47, 48); a thin-film support formed of stacked insulating layers (8a, 8b) is formed to lie over the cavity portion (5; 47, 48); characterized in further comprising: a first heating member and a second heating member both sandwiched between the insulating layers (8a, 8b) in the thin-film support; and a driving circuit as heating temperature control means configured to control the temperature of the first and second heating members (3,4) by supplying heating current; wherein the second heating member is located around a periphery of the first heating member, the heating temperature control means are adapted to control a temperature of the first heating member to be higher than a temperature of the second heating member, the heating temperature T2 of the second heating member is configured to be set such that T1• X4/X3+T3<T2<T1, wherein the heating temperature of the first heating member is denoted by T1, the heating temperature of the second heating member is denoted by T2, a gas temperature around the thermal gas sensor is denoted by T3, a distance from an end of the cavity portion to the first heating member is denoted by X3, and a distance from an end of the cavity portion to a center of the second heating member is denoted by X4; and the thermal gas sensor is adapted to measure a concentration of an ambient gas based on electric power applied to the first heating member. a first heating member and a second heating member both sandwiched between the insulating layers (8a, 8b) in the thin-film support; and a driving circuit as heating temperature control means configured to control the temperature of the first and second heating members (3,4) by supplying heating current; wherein the second heating member is located around a periphery of the first heating member, the heating temperature control means are adapted to control a temperature of the first heating member to be higher than a temperature of the second heating member, the heating temperature T2 of the second heating member is configured to be set such that T1• X4/X3+T3<T2<T1, wherein the heating temperature of the first heating member is denoted by T1, the heating temperature of the second heating member is denoted by T2, a gas temperature around the thermal gas sensor is denoted by T3, a distance from an end of the cavity portion to the first heating member is denoted by X3, and a distance from an end of the cavity portion to a center of the second heating member is denoted by X4; and the thermal gas sensor is adapted to measure a concentration of an ambient gas based on electric power applied to the first heating member.