A polypropylene film: (a) characterised in that a sum of stress at 5% elongation values (F5 values) for a longitudinal direction and a width direction at 130°C as measured by a method according to the description is 15 MPa or more, wherein for dielectric breakdown testing at 130°C, a dielectric breakdown voltage (V/um) after performing a heat treatment for 1 minute at 150°C and a dielectric breakdown voltage (V/μm) without performing the heat treatment satisfy the following relationship B 150 / B 0 ≥ 0.80; or (b) characterised in that for a relaxation time T2 of an amorphous component obtained by a pulse NMR (nuclear magnetic resonance) method according to the description, a relationship between a relaxation time (T2A) (μs) after a heat treatment for 1 minute at 150°C and a relaxation time (T2B) (μs) before the heat treatment satisfies the following formula T 2 B / T 2 A ≥ 0.90; or (c) characterised in that in a linear function ((Tmβ) = xβ 0.5 + y) obtained from a relationship in which a melting peak temperature (Tmβ) (°C) observed by DSC (differential scanning calorimetry) measurement as measured by a method according to the description of each of a film (hereinafter, referred to as a treated film) heat treated for 1 minute at 150°C and an untreated film (hereinafter, referred to as an untreated film) at a temperature raising rate β (°C/min) is defined as a Y axis, and a value (hereinafter, referred to as β 0.5) obtained by raising the temperature raising rate β (°C/min) to the power of 0.5 is defined as an X axis, a relationship between a y-section (H1y) (°C) of the linear function in the treated film and a y-section (H0y) (°C) of the linear function in the untreated film satisfies the following relationship H 1 y / H 0 y ≥ 0.90. (a) characterised in that a sum of stress at 5% elongation values (F5 values) for a longitudinal direction and a width direction at 130°C as measured by a method according to the description is 15 MPa or more, wherein for dielectric breakdown testing at 130°C, a dielectric breakdown voltage (V/um) after performing a heat treatment for 1 minute at 150°C and a dielectric breakdown voltage (V/μm) without performing the heat treatment satisfy the following relationship B 150 / B 0 ≥ 0.80; or (b) characterised in that for a relaxation time T2 of an amorphous component obtained by a pulse NMR (nuclear magnetic resonance) method according to the description, a relationship between a relaxation time (T2A) (μs) after a heat treatment for 1 minute at 150°C and a relaxation time (T2B) (μs) before the heat treatment satisfies the following formula T 2 B / T 2 A ≥ 0.90; or (c) characterised in that in a linear function ((Tmβ) = xβ 0.5 + y) obtained from a relationship in which a melting peak temperature (Tmβ) (°C) observed by DSC (differential scanning calorimetry) measurement as measured by a method according to the description of each of a film (hereinafter, referred to as a treated film) heat treated for 1 minute at 150°C and an untreated film (hereinafter, referred to as an untreated film) at a temperature raising rate β (°C/min) is defined as a Y axis, and a value (hereinafter, referred to as β 0.5) obtained by raising the temperature raising rate β (°C/min) to the power of 0.5 is defined as an X axis, a relationship between a y-section (H1y) (°C) of the linear function in the treated film and a y-section (H0y) (°C) of the linear function in the untreated film satisfies the following relationship H 1 y / H 0 y ≥ 0.90.