An elastic wave device (21; 41; 121; 141) comprising: a piezoelectric substrate composed of a rotated Y-cut X-propagation lithium tantalate single crystal with a substrate thickness from 100 μm to 350 μm; a functional section including a comb-shaped electrode provided on the piezoelectric substrate; a sealing body (27; 43; 127; 143) provided on the piezoelectric substrate, the sealing body (27; 43; 127; 143) sealing the functional section, having a glass transition temperature between 40°C and 90°C and confining a space above the comb-shaped electrode, the sealing body (27; 43; 127; 143) being formed by a material having 30 wt% of a heat-curable resin containing an epoxy-based component and 70 wt% of a negative expansion material having a negative coefficient of linear expansion for the operating temperature range of the elastic wave device (21; 41; 121; 141) between -55°C and 125°C, the negative expansion material being one of zirconium tungstate, Li 2 O-Al 2 O 3 -nSiO 2, hafnium tungsten oxide, bismuth nickel oxide and manganese nitrides having an inverse perovskite structure; and a cover enclosing the space, the sealing body (27; 43; 127; 143) covering an upper surface of the cover opposite a surface of the cover facing the space, with a coefficient of linear expansion of the sealing body (27; 43; 127; 143) being greater than a coefficient of linear expansion of the substrate in a first temperature region having a lowest temperature that is at least as high as the glass transition temperature and the coefficient of linear expansion of the sealing body (27; 43; 127; 143) being less than a coefficient of linear expansion of the substrate in a second temperature region having a highest temperature that is lower than the glass transition temperature of the sealing body (27; 43; 127; 143). a piezoelectric substrate composed of a rotated Y-cut X-propagation lithium tantalate single crystal with a substrate thickness from 100 μm to 350 μm; a functional section including a comb-shaped electrode provided on the piezoelectric substrate; a sealing body (27; 43; 127; 143) provided on the piezoelectric substrate, the sealing body (27; 43; 127; 143) sealing the functional section, having a glass transition temperature between 40°C and 90°C and confining a space above the comb-shaped electrode, the sealing body (27; 43; 127; 143) being formed by a material having 30 wt% of a heat-curable resin containing an epoxy-based component and 70 wt% of a negative expansion material having a negative coefficient of linear expansion for the operating temperature range of the elastic wave device (21; 41; 121; 141) between -55°C and 125°C, the negative expansion material being one of zirconium tungstate, Li 2 O-Al 2 O 3 -nSiO 2, hafnium tungsten oxide, bismuth nickel oxide and manganese nitrides having an inverse perovskite structure; and a cover enclosing the space, the sealing body (27; 43; 127; 143) covering an upper surface of the cover opposite a surface of the cover facing the space, with a coefficient of linear expansion of the sealing body (27; 43; 127; 143) being greater than a coefficient of linear expansion of the substrate in a first temperature region having a lowest temperature that is at least as high as the glass transition temperature and the coefficient of linear expansion of the sealing body (27; 43; 127; 143) being less than a coefficient of linear expansion of the substrate in a second temperature region having a highest temperature that is lower than the glass transition temperature of the sealing body (27; 43; 127; 143).